guitar hero 3 help

[kigmob]

I just got GH3 for my iMac and I'm not too happy with the game. I just meet the system requirements so I figured it would run alright, but the game seems to lag during game play like most people say. I did notice though that it doesn't get as bad as most people says it does. I can manage to get through a song with all the settings on the game set as low as possible. I have a 17" iMac, 2ghz intel core 2 duo, 1gb memory, radeonx1600 graphics, and 128 mb of video memory. I was wondering if getting more memory would help because that's about the only thing I can change to make it faster. Other than that I was just going to sell it because I ordered it from the Apple website and the return policy says they do not take returns of opened software. What should I do????!!!??!