how do i determine the windows xp version?

i have a client who is running parallels desktop 3 and xp doesn't load past a black screen. i am preparing for the possibility of doing a repair install, but she doesn't have her xp disk anymore. as i understand it, to do a repair install, the version of xp on the install disk has to be the same as the version on the hard disk. so, is there a way to determine the version of xp on the hard disk without xp being able to launch?