Hi Exautt,
Yep, this is an error commonly occurring when you add a drive with XP already installed to a system with Vista working just fine.
The problem is that the XP bootloader files are not on the Vista drive.
Set the XP entry in EasyBCD to the bootloader drive. Copy
the boot files to your boot drive and copy over the boot.ini file from your Windows XP drive to there as well - but be sure to update it to reflect the new position of the XP drive/partition.
It would help if you could go to Diagnostics | Copy Debug Data and paste it in your reply.