I know im shooting down the same tunnel as everyone else, but it is really really not worth it to upgrade that computer in any way. If you buy a new processor for it, even the best one it can handle, you will still be buying a worthless processor to put into a worthless board that you plan on upgrading later anyway... its stupid. I understand the excitement, but use this one as a tinker machine and nothing else, save up some cash and build yourself a decent machine down the road dont throw money down the proverbial toilet on this one.
Also, not to be a jerk, but I dont believe your BIG into pc gaming... because if you were you would know that this is not even close to the type of machine. You would also know that to stay up to date on pc gaming it costs A LOT of money. Anything graphics cards you buy are outdated... three months before you bought it and to run games at full settings your going to be throwing a lot of money into your machine every few years. You knew that though since your big into it.
Im not trying to be rude to you as a new member, but if 13 people just gave you the same advice, at least CONSIDER listening. You have a worthless computer, it was free and you have nothing invested in it... so dont invest in it! Invest in something new that you will actually enjoy and will actually benefit you. Anything... ANYTHING you do to this computer with the current machine will be entirely futile.