Sorry for the delay, I was offline for a bit. Of course I will toss these other answers in.
One thing though, if you are talking about upgrading, the processor the board , teh graphics card you best get a new machine.
For one, you cannot just connect your old hard drive to a new motherboard. You will need to reinstall everything and start from scratch. Since you would be doing that any way you may as well upgrade the hard drive too, and then just get a new machine.
Now if you are not ready for a new one yet and you want to me able to game on this one, the processor and the video card should help a bit.
It looks your motherboard has an integrated graphics card meaning it is built into the board. However you do have a PCI express X16 slot in there so you can upgrade.
I had one of these for a long time, I think it cost like over $300 when I bought it but since it is old the price is way down. I liked it a lot. Have a look here:http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=6896097&csid=_61
That would be a good upgrade to the card that is in there now. If you upgrade the processor and the card you should be able to play games, I cannot say they will run well but they will run. It really depends on the game. The processor I linked you above is one of the first dual core processors that came out
If you have never upgraded a processor before be careful. Make sure you search out some video tutorials on youtube to get an idea of what you need to do. It is not that difficult but you can mess things up if you make a mistake. I would suggest you make back ups of your hard drive before doing any hardware replacement just in case.
Have a great weekend.