Well I have Windows XP 32-bit. I want to add more RAM to my system since I only have 2GB at the moment, but I've heard that I will not be able to use more than 3GB on my system unless I upgrade my OS. If I buy a single stick of 1GB RAM and add it to my existing sticks will it force my computer to use Single-channel memory since it is an uneven amount, or should I buy two 512 sticks and fill up all my RAM slots... of course I could upgrade to XP Pro 64-bit or even Vista but I'm not sure if I want to do that yet. What would you guys do in this situation?

really, no ones going to reply?

I'd leave it at 2gb for now. When you're ready to upgrade to xp 64 or vista 64, you can also upgrade the ram then.

some questions for the op, are you running programs that use up 2 gigs of ram, is your hard drive busy with page file writes, have you checked task mgr when your computer is loaded down with what ever it is that you do with it?
if yes then you could use more ram, if no then keeping dual channel ram is your best bet.
also alot of motherboards work much better with even pairs of ram sticks some wont even work at all with an odd number.

I use my computer mostly for gaming so the more RAM the better. I think I'll just upgrade the OS seeing as I will need to eventually anyway.

Since you're playing games and >2gb may be needed, upgrading the OS is a good idea.