My computer is running slowly. I think it is wasting memory.

I'm running 11.04 on a 7 year old Dell Latitude D610 laptop. When I first installed Ubuntu, it breathed new life into a computer that had slowed to the limits of usability. It slowed down over time, but it returned to its best performance when I formatted it again while I was upgrading to 11.04.

Its gotten pretty slow once more. I suspect I could restore it again the way I did before, but is there a way to remove all the crap slowing down my computer without wiping the whole thing clean?