Yes you can if your BIOS supports dual booting. I have done that with my AUSUS 8N32-SLI-Deluxe. When you start your computer with the Vista CD inserted it will perform checks and if you have 2 drives it will ask you which drive do wish to install it. Simply select the non XP drive. Be advised that they will be separate operating system on the same computer, you can't work on Vista files if you booted to XP and visa versa. They will both install on a C: drive letter....but they aren't on the same drive.
Can you put Vista on one drive and leave XP Pro on another drive and switch on boot to which one you want to use?
My Computer is good to go with Vista... Everything is to spec...

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic