How to change PC's boot (XP --> Vista)


I've got a problem. Hopefully a minor one to fix:
I got the following hard drives: 80 gb, 120 gb, 120 gb. MB: Asus p4c-800 e-deluxe.
I've installed win vista on one of the 120 gb while I already had xp on the 80gb. The Bios is configured to boot from the 80gb. When I start the pc, I can choose between xp & vista. When I change the Bios configuration to boot from the 120gb, it stuck. Nothing boots. I tried using EasyBCD and I configured that Vista would be the default os. I still can't manage to disconnect my old 80gb and configure the boot to the 120gb.
Many thanks,
Hi Eldad,

You should NEVER change the order of the drives from the BIOS. Ever.

That said, you won't be able to boot from the 120GB because it doesn't have the MBR or the boot files installed.

I do not understand why you need to change the boot order though, you should just set up the Vista bootloader on the 80GB drive, and configure it with EasyBCD to boot into either XP or Vista, no problem.