I was given a Mac G4 without the operating system. It had Mac OS 10.4. Is there an Ubuntu version I can use for the Mac like there is for my PC? If so, what version? And are there any special tricks for Mac? Or is it fairly simple as it is for PC. (I'm not at all familiar with Mac, but the components look pretty much the same.)
The PowerPC version of Ubuntu, which is community-supported rather than officially supported, should run on your Mac that has a G4 processor. There are some differences between the PowerPC version of Ubuntu and the versions of Ubuntu for officially supported architectures; you will likely find the PowerPC FAQ helpful. There are also some very general system requirements.
The PowerPC download page contains links to where you can download the PowerPC version for each Ubuntu release, as well as links to special installation instructions, as applicable. Please note that for some Ubuntu releases, the PowerPC version's desktop .iso image is too large to be burned to a CD, so it must be burned to a DVD instead (or written to a USB flash drive, if your G4 Mac is capable of booting from one).
I have just loaded Ubuntu 12.04 on my iBook G4 and it runs great. Everything is working except my Airport card, I'll work on that tomorrow. You can download Ubuntu from this link.
Scroll down the page and double click on the file ubuntu-12.04-decktop-powerpc.iso.