See if the following article helps explain why you are not seeing the full 4GB RAM in a 32-bit Vista system: The system memory that is reported in the System Information dialog box in Windows Vista is less than you expect if 4 GB of RAM is installed
. Seeing 3.2-3.3 GB is common and not indicative of a problem with your system (nor is there much you can do to change this).
I don't know if gaming performance is better with 64-bit systems or 32-bit systems if both have the same amount of RAM installed and the same video cards (with the same RAM on the cards) and the same other hardware performance characteristics (like the speed of the hard drive, the refresh rate limits of the monitor, and other such things). I suspect the 64-bit system may be a little faster all other things equal on some games and no different on others but that's just an educated guess (assuming you have a 64-bit processor and motherboard). Of course, if you add more RAM to the 64-bit system (something you can't do with a 32-bit system) and increase RAM on your video card, you will probably see some improvement - if the rest of your system can handle it and all the other devices are "enhanced" so nothing is causing a bottleneck (like maybe a slow monitor or something like that).
I hope this helps.