well he could plunk in a G4 cpu upgrade but that would be the same thing really
the best things he can do is max out the ram ( 1,5 gig ) or at least more ram
turn off dashboard and spotlight
get a better video card
and thats it
or take all that upgrade to a faster G4
think of what you will spend on all that and look in to a used G4 mini
unless off course he likes to have a blue yikes!