You shouldn't disable it. If he is getting it repeatedly turning up on boot then there is either a problem with drivers/hardware or he is not shutting it down correctly.
Get him to run a full chkdsk on each drive when windows is loaded and this should sort his problem. I think it asks if you want to run it or not each time you skip it on boot so you could just leave it to run the next time he boots.
I was just checking (with my previous question) that it was on boot because I have used XP for months on multiple machines in anger - overclocking, fiddling etc - and have never managed to get a chkdsk on boot.
Ritchie, Thanks for the advice, i will find out it he is just goofing off and not caring how he shuts down or there is some other problem! ALEC, Thank you very much for those instructions, i will print them out and keep them for future reference for myself, TOM