Be aware that all the PowerMacs are pretty much dead in the water for many modern web pages. The technology in those pages abandoned the "G" series processor long ago. I keep my G4 Tower limping along on the Web by using TenFourFox. Web sites see it as a reasonably current version of FireFox--newer than any version of FF that will run on a G-series--so you don't get all the "this browser is not supported" messages, but current versions of TenFourFox do not support plug-ins so you can't run Flash player, meaning no videos will play that rely on Flash.
http://www.floodgap.com/software/tenfourfox/
If you go for a G4--they are indeed lovely to behold--I recommend going for the latest version with a 1.25Ghz processor. Theose also have USB 2.0 so are not so sluggardly with backups to external drives. They can also handle up to 2GB RAM with teh proper models.
Here are my "big" caveats:
1) The G4 iMac was never inteded to be user-serviceable. If you have to max the RAM, replace the hard drive or the optical drive, or even chenge a little $5 internal backup battery, it is a major teardown that is not one for the average user. Failing to reassemble to strict requirements can cause the computer to overheat and fail. If you are not up to the challenge and seek outsire help, be aware that Apple no longer will do any work on the G4 iMac.
2) Software: Almost no new software will run on a G4 Mac. You will be searching for used packages contemporary with a 2004 computer. Office 2004 is the sweet spot for that one. However, Office 2008 will run on a G4, G5, or an Intel iMac.
3) Check the chrome display arm carefully for proper movement and that it stays in place. After 10+ years, many are now rather "tired" and droop unattractively.
