You need to provide more information.
Did this Dell originally come with XP installed? What does it say on the
COA sticker (do NOT post the product key!)?
Is the new hard drive hooked up correctly? How exactly did your buddy
attempt to install Windows XP -- especially since he doesn't have the
installation CD? Also, what is the model and model number of this Dell?
Knowing that would be helpful to find out the original method Dell
provided to the end user to reinstall the OS. BTW, it will be one of the
following methods:
Installation CD (Dell calls these Reinstallation CDs)
Recovery CD (this contains an image of the hard drive as it was the day
it left the factory)
Recovery Partition (the old hard drive that is out of commission may
have contained the sole means of restoring via a hidden recovery
partiton -- a poor method for obvious reasons!)
Dell might be able to provide installation media. If not, many people
have reported success with this place:
http://www.restoredisks.com/