I recently acquired a iMac G5 PPC
it had a broken screen which you can pick one up on ebay for around 40 quid, i fitted the new screen in about 15 minutes not a hard job at all, noticing how good the apple hardware really is built compared some of the crap sold on the market today!
Because the operating system is no longer supported for PPC then the way to go is linux, after trying various flavours of ubuntu and failing miserably i tested debian, now i havent used debian for a while but it went on no problem and run slick as you like. The only problem was the machine was getting hot as its having to work a bit hard that usual !! so i ordered a fan of ebay with speed control and got a local engineering firm to cut the hole and i fitted the fan – i have to say it works flawlessly and its not noisey at all!!
it runs a full blown cctv zoneminder server and runs as our home juke box nicely and looks amazing 🙂 if you get chance to grab one get debian on it but youll need that extra fan!!