I bought this Mac Pro w/ Leopard used and iTunes comes up every time I boot. How do I prevent iTunes from autorunning? I've looked everywhere I can think of but no luck.

System Prefs, then check the section which details the users.. Can't recall the item, once found. Then select the user you logon as and checks it's logon items. You should see iTunes in the list. Remove it.

"System Preferences -> Accounts -> Login Items" and remove iTunes

I don't think you should be allowed to own a Mac Pro if you didn't know how to do that.