As far as i know, all the drivers will be in place, because the drivers are from the OS, not the BIOS/processor, and the intel version of OSX is, as I was lead to belive wilst watching the keynote, exactly the same as the PPC one.
I am in almost the exact same boat as your friend, only thing is that i've had my iMac 9 days and have used it, though im still rather confident I am getting a replacement either from Apple of John lewis. I would 100% change it for an intel, no doubt about it.
As far as 64/32 bit goes, you have two cores in the intel, so 32+32=64 hehe (i know im talking total crap, but what the hell :-)) On a serious note, I really dont rekon you would notice a speed difference between 32/64 bit, expecially when doing relativly non processor intensive stuff like garageband.
As I say, if i were in your friends boat (and I kind of am..) then I would (and am going to try to) swap if for the new one. At least then you have a much speddier machine, and the newest thing out