Odd that you're having such problems. I've had my iMac G5 running 10.4.5 without any issues. Depending on the G5 system you have, it's possible that you need a firmware update. See the link below for the firmware needed for your Power Mac G5 (if needed).
http://docs.info.apple.com/article.html?artnum=86117
What I don't understand is why you would join just to gripe about your OS X system and say you're selling it? I'm guessing maybe if you want someone here to purchase it from you. In that case, there is a Classifieds section where you can sell the G5. Other than that, it just seems like a waste of energy to just complain about it here. Just sell it to someone who would make use of it and get yourself the PC you want.....that's it....