Upgrade help!

I currently have a crappy integrated thing useful for office work and not much else. TF2 just about runs on it averaging about 20FPS(ouch)

My original specs are here(I've added RAM but that's it)http://h20000.www2.hp.com/bizsupport/TechSupport/Docume...

I'm also considering a CPU upgrade so if that will change what I could use then let me know
What would be the best to put on this motherboard for proper gaming?
I don't really have a budget, I'm just interested in what I could get of if my whole computer needs upgrading.
Thanks