Trying to "Un-RAID"

Someone please help, or at least explain what's going on.
I originally built this computer with XP32 installed on two RAID1 drives, RAID setup was done using an Intel ICH7R controller on the motherboard, worked fine.
Later added Vista32 to an external SATA hard drive and would dual boot as needed, no problem. I never used Vista very much.
I decided that it was time to wean myself away from XP and start using a more up to date operating system such as Win7, in the 64bit version since that works on my laptop and I get the impression that I need a 64bit operating system to take advantage of the 4Gb memory I have installed.
I want to do a clean install of Win7 64 on the external drive, undo the RAID but keep XP on one of the drives while replacing the other drive with a 1Tb drive for data storage. I now realize I dont really have to set up a boot loader because the external drive has an on/off switch - if I set that drive up as the first one in the BIOS I can choose my operating system by simply toggling it on or off before starting the computer.
Question 1: Does this plan sound feasable?
The problem I have run into is that after turning the external drive off, resetting the internal drives to non-RAID in the Intel "Matrix Storage Manager" available during POST and setting the BIOS "Configure SATA as..." option to AHCI instead of RAID the computer booted into XP fine but after a little while gave me a message "Windows has finished installing new devices. The software that supports your device requires that you restart" etc. If I do the restart it tries to boot into XP, crashes, and reboots in an endless cycle. To get the thing to boot into XP I had to "Configure SATA" as IDE and boot into "Last known good confuguration". Luckily I can boot it up! Also the computer only shows one hard drive, why not the other one?
Question 2: what am I doing wrong? There are a lot of posts on the internet about setting up RAID but not very many about getting rid of it. Before I did this I checked the Intel website and they said it was ok to undo a RAID1 and that there wouldn't be any data loss either.
Easy question 3: I assume I use EasyBCD to get rid of the pesky XP/Vista boot menu?
I would appreciate it if someone could shed some light on these questions - sorry about the long winded exposition...