If it is a G5 iMac, forget it.
On the other hand, installing another HD into a PM G5 is something that Apple has deemed as a "user upgrade" and as such, have posted information on their website as to how to do it.
You did look at the Apple site? Of course not. You expected others to do your research for you.
OK, because I'm in a good mood and your Google search engine is broken, I decided to take 5 seconds out of my busy Sunday, go to the Apple site, Support, enter "adding HD" in the search box and coming up with this:
See, it's not that difficult, is it?
Does anybody know of a website that has an article on how to add a hard drive to a G5? I don't know anything about upgrading but don't want to pay anybody because I don't immagine it being to complicated. Any help would be appreciated.