Mike--
It's really best to install the older OS first. You have a much better
chance of going without a hitch. However, I thought I would add a link we
use a lot here for dual booting when Vista is already in place but I do dual
boots all the time and I wouldn't do it without installing XP first.
Dual Boot Instructions for XP and Vista Dual Boot
http://apcmag.com/5023/dual_booting_xp_with_vista
You'll get the option to boot to either Vista or XP and it will look like
this:
http://www.theeldergeekvista.com/images/Vista Dual Boot Installation/Vista Final -0037.jpg
Best to shortcut from Vista desktop to XP desktop once you install the
dual boot, because if you boot to XP you will lose your Vista restore points
unless you encrypt them with Bit Locker(there are other methods to protect
the Vista restore points discussed on this and the general group) if you
have it on your Vista edition. (I rarely need to go to an XP boot on a dual
boot because you can access XP from the Vista desktop this way:
C: (or whatever drive)\Documents and Settings\Milhouse' Profile\Desktop and
if on XP you can go to Vista Desktop via this path:
Vista Drive\Users\Milhouse's Profile\Desktop
I am a dual boot proponent because you always have your months or years of
accumulated docs, settings, shortcuts, files and folders from XP on the box.
Why waste time and energy transfering and copying when you don't need to and
you can drag the icon on the top left of the folder that shortcuts to either
and put it on the desktop and click it when you want to access the other
desktop.
Best of luck.
CH