Hi All,
I have just built myself a new computer. One of the final things I need to add is some more RAM (as I currently only have my old 256Mb of RAM in there). I want to add an extra gig for now and was wondering whether it would be better to add 1x1Gb stick or 2x512Mb sticks or doesn't it make any difference? I have 4 slots so I'm not short of room I just want the best performance.
Thanks for your time.

Well, it depends . Does your board support RAM in Dual channel mode? If yes, get two identical sticks of 400MHz. Preferably matched pairs from Corsair or Kingston. If your board doesn't support Dual Channel, I'd still recommend 2 sticks simply because if one of your ram sticks goes bad, you can still run the computer on the other stick.

It's slightly better to buy 2x512 MB, I read it somewhere but don't know why !

If you have 4 slots then you have a dual channel capable mainboard - on the AMD side S754 single channel boards all have no more than two slots, and all socket 939 AMD and current P4 boards are dual channel. It doesn't matter if you go with 2x512 or 2x1G. If you have the money to do 2x1G i would do it, especially for the sake of possibly running Vista in the future.