Adding another 0.1 GHz, 1GB ram and a new graphics card would totally suffice for NFS Most Wanted at lowest settings. Just saying.
However it would be a good idea to buy a fully new one, (whenever pr0n starts being in HD 2048p you'll need it anyway).
However in my opinion 4GB ram totally are enough if you're just gaming, (except you try to play Death Rally 2012) also i myself wouldn't consider getting integrated solutions, because it's not really efficient to upgrade or replace them, however this might only be mho.
It might be an idea to look out for one with SSD's, i tested a double raid of these at a friend's, and they work pretty awesomely. When the support and the sturdiness of those improves any time soon, get those. The future speaks SSD.