IIRC, a lot of G5s had overheating problems. I'd keep a close eye on things.
A quick rundown on Macs. If you have any specific questions, I know a fair amount off the top of my head and if it exceeds my knowledge, I will have access to a 10.2 machine the day after christmas. This is all based on memory, I've not used an OS X machine in a long while.
As for stats on all G5s:
http://www.everymac.com/systems/apple/powermac_g5/index-powermac-g5.html Basic stats for your machine can be found under the apple menu -> About This Mac. Should show basic RAM and CPU specs. If you want some advanced information, go to Hard Drive -> Applications -> Utilities -> System Profiler. You can get craptons of information from here.
If you're keen on Unix, the Darwin terminal (Hard Drive -> Applications -> Utilities -> Terminal) might be of interest to you but really isn't that useful for anything but power users.
System preferences (Apple -> System Preferences) is fairly straightforward.
I don't know how much of your Apple virginity you've lost thusfar, but here's an important thing to remember that a lot of people forget, especially those that primarily use PCs: Quit your programs, don't just close out of them. Command + Q will completely quit the program, if you just x out of it it will keep running and using up your valuable memory. A rather small black triangle above the application in the Dock will let you know that the application's still open.