If you never need more then 2 GB of ram then you will be faster to have 2GB then 3GB but if you use more then 2 (Video editing advance gaming) then the more ram is better because you will be using the Hard drive less.
i added 4gb to my system not long ago when i installed windows 7 64-bit. i had 2gb previously installed. i found after that i never even used 2gb completely, except when stress testing. also one of the new sticks was bad, so it was an easy rma refund choice for me. i have noticed 0 difference in 2gb and 6gb, even in gaming; i think cod4 used the most memory and it combined with normal windows 7 operation was only using 1.7 or 1.8, but the only way 6gb could come close to being used was by having multiple instances of prime95 or cod4 open simultaneously, at which point the processor would never be able to keep up. i think most people get more RAM than they need actually...i only got it because i thought 64-bit meant since i could handle more, may as well get it, when in fact it wasn't being used at all.
so, i don't think it's going to be worthwhile at all for you to use that extra 1gb stick you have lying around.