My general comments are in your other thread
here, but no, you aren't stuck gaming at 800x600 on Mac
🙂
I usually game (widescreen) at 1280x800 or 1600x1000 on my iMac Core 2 Duo 2.33 with nVidia 7600GT. idTech 4 games look great!
(Some games that don't happen to list the resolution you want can be modified by editing a text file.)