Yet another Mac

Someone on Freecycle gave me an early iMac G5 - it's missing its hard drive and may have other problems, so I want to proceed with great caution, so that I don't buy e.g. a drive it can't use. So far I've got it to boot off the OSX 10.3 CD that came with it, until it reaches the point where it wants to access the hard disk, which tells me that it's got some RAM, and that the screen, mouse, and keyboard work. Is there anything else I should be checking out before buying a drive?

later - looks like I can get a 500gb drive for £15, might as well get it - if the mac is no good, I can shove it in a housing for use as an external drive.