I want to upgrade the RAM on my Dell D600 lappy. Its 256 X 2 right now. I'd like to get 1GB and replace one of the 256 rams. Somewhere I recall reading somewhere it is best to have matched MB pairs. I dunno. Will I run into problems running 1025 and 256 ram??? Within a few months went the $ are right I would replace the other 256? Thanks, Jack