http://www.g5drivebracket.com/That's the one I bought, Gary. I'm not sure whether I'd pick that one rather than any of the others, but at the time it was either that or the billion dollar Wiebetech one that was ludicrously expensive - which I didn't even consider.
The bracket holds three over the two in the normal drive bay, but I only have two (total four drives) in at the moment. I'm not using RAID or anything exotic - I just needed extra storage. However, I'm about to put a 36GB Raptor from one of my Windows machines in there as well (I'm replacing it with a 500GB drive in that machine and may as well use it).
I'll post if I have any heat problems, but it seems unlikely that I will.
Oh, and a tip: if you install a bracket in your G5, do a search on the Apple site to see how you remove the optical drive. You need to get it out of the way so you can plug in the power cables you need to run over there. It just unplugs from the motherboard and slides right out, but it may take a slight tug the first time and you'll be stuck if you don't know how it works.
The instructions for the drive bracket go into too much detail about everything but that, and it's the only thing that's not entirely straightforward. It would have taken me ten minutes if I'd known about that, but instead it took me over an hour.
It's true that I'm not mechanically inclined - in fact I'm a total DIY putz - but this certainly isn't beyond even me. [:)]