With all due respect to the posters on this page, most of the advice given lead to ineffective solutions to the problem. I'm afraid you can't do much to boot off of it, unless you do a re-install, and even then, I wouldn't bet my life on it. But here's what you can do next time if you want to move a working partition to another computer, and you still want to boot off of it, as you naturally would have.
First, for some basics. When you try to boot a partition that's been transferred from one PC to another, he will get what is known as a "STOP Error". In essence, his PC will just auto reboot itself just after the BIOS screen finishes making its appearance, and it will continue this mode of rebooting itself for an infinite number of times. Why does this happen? The registry entries and the drivers for the mass storage controller of his old system's OS won't be the same as it should be in the new system. Thus, the new system crashes with no end in sight. What can you do in advance to avoid this? Follow these simple steps
1) Copy the following information into Notepad, and then save the file as Mergeide.reg, without the .txt file name extension.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\primary_ide_channel]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="atapi"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\secondary_ide_channel]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="atapi"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\*pnp0600]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="atapi"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\*azt0502]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="atapi"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\gendisk]
"ClassGUID"="{4D36E967-E325-11CE-BFC1-08002BE10318}"
"Service"="disk"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#cc_0101]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_0e11&dev_ae33]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1039&dev_0601]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1039&dev_5513]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1042&dev_1000]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_105a&dev_4d33]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1095&dev_0640]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1095&dev_0646]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1095&dev_0646&REV_05]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1095&dev_0646&REV_07]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1095&dev_0648]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1095&dev_0649]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1097&dev_0038]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_10ad&dev_0001]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_10ad&dev_0150]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_10b9&dev_5215]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_10b9&dev_5219]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_10b9&dev_5229]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="pciide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_1106&dev_0571]
"Service"="pciide"
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_8086&dev_1222]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="intelide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_8086&dev_1230]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="intelide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_8086&dev_2411]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="intelide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_8086&dev_2421]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="intelide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_8086&dev_7010]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="intelide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_8086&dev_7111]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="intelide"
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\CriticalDeviceDatabase\pci#ven_8086&dev_7199]
"ClassGUID"="{4D36E96A-E325-11CE-BFC1-08002BE10318}"
"Service"="intelide"
;Add driver for Atapi (requires Atapi.sys in Drivers directory)
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\atapi]
"ErrorControl"=dword:00000001
"Group"="SCSI miniport"
"Start"=dword:00000000
"Tag"=dword:00000019
"Type"=dword:00000001
"DisplayName"="Standard IDE/ESDI Hard Disk Controller"
"ImagePath"=hex(2):53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,\
52,00,49,00,56,00,45,00,52,00,53,00,5c,00,61,00,74,00,61,00,70,00,69,00,2e,\
00,73,00,79,00,73,00,00,00
;Add driver for intelide (requires intelide.sys in drivers directory)
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\IntelIde]
"ErrorControl"=dword:00000001
"Group"="System Bus Extender"
"Start"=dword:00000000
"Tag"=dword:00000004
"Type"=dword:00000001
"ImagePath"=hex(2):53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,\
52,00,49,00,56,00,45,00,52,00,53,00,5c,00,69,00,6e,00,74,00,65,00,6c,00,69,\
00,64,00,65,00,2e,00,73,00,79,00,73,00,00,00
;Add driver for Pciide (requires Pciide.sys and Pciidex.sys in Drivers directory)
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PCIIde]
"ErrorControl"=dword:00000001
"Group"="System Bus Extender"
"Start"=dword:00000000
"Tag"=dword:00000003
"Type"=dword:00000001
"ImagePath"=hex(2):53,00,79,00,73,00,74,00,65,00,6d,00,33,00,32,00,5c,00,44,00,\
52,00,49,00,56,00,45,00,52,00,53,00,5c,00,70,00,63,00,69,00,69,00,64,00,65,\
00,2e,00,73,00,79,00,73,00,00,00
=- THE END. (DO NOT COPY THIS LINE!) -=
2) Extract the Atapi.sys, Intelide.sys, Pciide.sys, and Pciidex.sys files from your Windows\Driver Cache\I386\Driver.cab file, and copy the files to the Windows\System32\Drivers folder. You do need all 4 of these files for the procedure to succeed. If any of these files are for whatever reason not present, you may extract them from any Windows XP CD, specifically from the i386/Driver.cab file.
3) Time to check back with our old Mergeide.reg file. Go back to the location you saved it and double click it. It will prompt for permission regarding a registry change. Just hit yes.
4) That's all. At this point, you can make an image of this partition and expect to boot off of it after moving it to another system, etc. On your first boot on the new system, you will be bombarded with about a zillion new "Add New Hardware" prompts due to all the new hardware XP thinks has been added at once. :??