Well, it sounds like you have Classic automatically starting up when your iMac is booted. To solve this, open System Preferences, choose "Classic", and then there should be an option to turn it off there. (I'm not completely sure, because I'm not at my G5 right now.)
As for your other problems, I'm not really sure. Try opening the System Preferences -> Accounts -> Login Items, and see which items are starting up. I have like 2 items in there, but if you have something like 10 in there, then that could be the problem too.
John A
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