What Windows "Experience Rating" tells you shouldn't be what you take into the highest consideration. Play some games etc and see if it's better than what you had stock.
What experience you get playing games is the thing to look at as said. Fur mark etc is ok for a base benchmark to compare future upgrades against but i wouldn't use it as a marker for how good a PC is in general.
just download something called winbubble
here: http://www.pcworld.com/downloads/file/fid,70407-order,4/description.html
leads to the pcworld article. download is on top.
after installing, go to the specific tab, and select hacking WEI score from the buttons. it's the top left button.
then you can set your WEI scores.