people overemphasize the need to have matched pairs of ram. it is nice if it will logically suit your needs. however, it isnt always the best move. if you have a 512, and are thinking of upgrading really think about it. if you add a 1gb stick you wont get the matched pair benefit. BUT if you plan on going up eventually to 2gb then you should NOT match them, but rather buy a 1gb stick, and then later on another. the speed difference is nothing huge.