Overclocking: just search for how to overclock on Google.
It's fairly easy to do if you don't go too far - once you get into voltage modding it gets too scary for me.
Just make sure you monitor your temperatures, and take it slowly.
A better heatsink/fan would be about £10 (probably around $15-$20?) - a good investment even if you're not planning on overclocking, as it will probably run quieter than stock and cool your CPU better.
I haven't tried NFS:MW, but
here's a review which includes the min. requirements and the results on his system, which is slower than yours in some ways and better in others - more RAM, slightly better graphics, weaker CPU.
I'd say your PC should be up to it, although it may not run on max. settings very well.
Stick to medium and you'll be fine.
Hope this helps.