what version of windows are you running?
IF the computer is telling you you need RAM, then you need ram. If you didn't install any new programs and it just started telling you that it needs ram out of the blue, then you have a virus and/or a trojan horse. Keep this in mind..no anti-virus program is 100% percent effective, especially the ones that were release before 2006. If you are using any older than that then you need a new one. avast.com provides a good free one that I used.
Sorry for the long post but the fact is...you need a ram upgrade...even if you have a virus or not.