What you are asking about is Virtual RAM, normally a laptop or desktop will allocate a certain amount (usually a gig or two) automatically. You can increase that as you said, and some games will take advantage of it. It will be a slight increase, but not a huge amount. Other games will ignore it completely.
It will also depend if you are running embedded graphics or have a dedicated card in your laptop. Try to allocate some and use FRAPS, see if it works for the games you want to increase performance on.
Link for details: http://www.ehow.com/how_5080005_allocat ... emory.html