You can use any mini-book or laptop for competition. It doesn't have to be from FIRST.
You only need to:
So Windows 7 Starter won't let you create a second user account?
I don't have any experience with Windows 7 Starter, but someone here can probably help if you tell us the steps you took, and give us the first couple of error messages you got.
Nothing wrong with switching to XP as long as you have an extra license around.
You will have to locate the matching hardware drivers for that model minibook for a different OS to work properly.