I have taken on a side job doing some tech consulting work for an Architectual firm. Most of the computers that they use are macs. I was looking on ebay to buy a used g4 to try and learn some of the basics. Plus I've always wanted to learn how to use them. I found a few that do not come with an OS. I was looking at just buying a copy of OS X also off of ebay but I'm unsure what to get. Any suggestions? thanks in advance.