I would like to upgrade the RAM on my girlfriends' parents' computer. They currently have 256 MB and their computer uses a 240 MB page file just when idling on the desktop. I used crucial's memory scanner and it gave me several types of memory, including variations that came in 256, 512, and 1 GB capacity. I don't think that they would ever need 1 GB for the tasks that they do; however, 512 would probably be good. I've heard though that mixing different capacity RAM can cause stability issues in programs. Is this true?