Oh crap! I just looked it up. Vista only makes you have a Windows.old folder
if you tried to install it on the same drive/partition as Windows XP. It
renames your old Windows folder as "Windows.old". You're in bad shape if that
happens! Basically, what you'll have to do probably is rename the Windows.old
folder (it is a folder, right?) back to "Windows", assuming that was it's
original name, and put that folder back where it came from (your first hard
drive). You'll probably have to move the Vista folder to the second hard
drive first (thus making Vista inaccessable).
Once the old Windows folder is back, you'll probably have to pop in your
Windows XP CD, boot from the CD and do an OS repair. If you're lucky, Vista
didn't completely destroy your copy of XP and you can get XP up an running
without re-installing it. If you're not so lucky, you'll have to re-install
XP.
Here's a tip for anyone who is installing a beta OS... DUAL BOOT! That way
you can use both OS's on the same computer. Here's how (only works if you
have more than one hard drive or partition): Your original OS should already
be on your first hard-drive. When you try to install Vista, pick Custom Setup
and instead of installing it on the same hard drive as XP, install it on your
second hard drive. Vista will automatically configure your compuer to use
both OS's. Once Vista is installed, it gives you the boot menu and you just
pick which OS you want to use. It's as simple as that!