XP is no longer supported. Some versions of XP SP3 would wipe out entire drives.
OS X Lion 10.7 only supports Windows 7 or later.
XP would be fine in virtual machine like Parallels or Fusion or VirtualBox
27" imac has a special tech note article (also all the FAQ etc is here too):
Mr. Wijnsma wrote:
Ok, i managed my why out. Now i'm in the second stage of installing windows xp. Right now it seems to work fine? Or do i have to delete windows xp again and just install windows 7?
It finally got out after rebooting like 20 times.
Tell us what version of OSX this is and you can get advice tailored for you, I can't divine version numbers ....