You can even add another hard disk and make a dual boot install, leaving your XP intact just in case you'd find something you can't do with Win7.
How do you boot to a different physical drive (without selecting it in the BIOS)? I've seen reference of boot managers allowing different OS's in different partitions on a single drive but I don't think I've ever come across two drives with different OS's and a way to select which to boot to.
(I am getting ready to supplement XP with another OS, probably Linux, and do surfing, email, etc with the second OS, so I'd be interested in the techniques.)
Also, a question for Skuzzy: will the coming version of AH support XP and DX9 for the foreseeable future? (So I don't have to buy Windows 7, or, heaven forbid, Windows 8.)