Why do you have 8GB of RAM running a 32 bit version of Windows? I assume you are dual booting with a 64 bit OS (unless you meant to write 64 bit above).
If it really is a 32 bit version of Vista, you can just leave the edit in place. Windows (or any 32 bit OS) is only going to be able to see 4GB of RAM, and after it gets done handing out memory addresses to hardware devices, there will only be about 3-3.5GB RAM available. Dropping down to 3GB of RAM is probably not going to effect performance much, so you could leave the edit in place until you finish the game, rather than switching back and forth each time you play.