if you can get his dash to load then you can copy the gamesaves off the HDD using a memory pack, and then go about installing a new HDD as normal. But does he use LIVE?
I assume so because he has PSO save games. This could cause problems as LIVE will detect that his xbox has god a different HDD installed and will BANN that xbox from LIVE.
So you will need a new eeprom for the new HDD too.
Sorry if i have confused you with all of this. =P