Did he do a quick format, or a full format.
If it was quick then you may be able to run a live linux disk and see if you can use a data recovery program to get the stuff back.
Another idea would be to put the disk in another computer already running an OS and try and run a data recoverer.
Dont install XP, as it may overwirte any residual data from the last format, leaving it irrecoverable.
Btw. if he did a full format, all the data has gone.
Hope this helps