The demo is here:



Quote from Mac Rumors message board: So I have been playing it for a while and it's a blast. What sort of frame rates are people getting. On my Dual/GHz/DDR PowerMac with the OEM G4MX 32MB I am getting a whopping 20FPS max at 800x600 at 32bit with all details turned on. With everything off and at 640x480 at 16bit I get 60-80FPS until I get in a fire fight and it drops to 20FPS. It is amazingly still playable at the low FPS and I was kickin ass but I want my ATI9700.