Hi there, I bought a G3 off ebay too, lol, I went to a site
www.macupgrades.co.uk it's really good it's really easy to follow the upgrades.
It also depends how much you want to spend, I have Mac OSX panther, 512mb Ram and an 80 gb hard drive, runs alot quicker, not as quick as a new machine but okay for me. Hope that helps, prank5ter.