Win7 32bit or 64bit for playing games.

Yes, 64bit has a huge difference. Performance improvments, better graphics etc. There are certain games that don't run on 32bit machines, so 64bit is a must.

64 bit ,since i think you'll use more than 3gb for gaming :P

32 has better performance and less memory usage for any game that requires no more than ~3.5 GB of memory, and also if you have less than that in total RAM memory in your PC.

64 is the only proper choice if you have 4 GB of RAM or more.

64bit, always. Otherwise your CPU won't work as much as it can and your ram will be capped

64bit is required for a lot of games, but honestly, the version you use should be based on your total memory. 32bit if you have 4gb or less RAM, 64bit if you have more.