Well, it depends on your os, i heard that xp can't handle anything pass 4? or are you running vista (boo)?
if you are running xp see upgrading to 3, even 1gb can help alot
Another way is to enlarge your swap so you can run and then your computer will auto dump all of the other memory into the swap freeing up a bit more ram for you. and the for the swap it uses your hd, so you don't really need to increase the number of ram you have, cheapest way possible