4GB of ram would greatly factor into the decision for me. Go with 64 bit so you don't lose usable memory due to hardware devices taking up address space.
You shouldn't encounter any issues with current games at this point, and unless you are going to play 16 bit games, I doubt you'll have compatibilty issues.
In terms of performance, both nvidia and ATI seem to have mostly stable drivers and their development efforts are probably not in favor of 32 bit at this point and certianly leaning towards 64 bit. The performace difference between 32 and 64 bit is virtually nonexistant.
But, with 4GB of memory or more, games that can use up significant amounts of memory will likely perform better with 64 because of the additional available memory.