What games are you trying or want to play?
In the long run if you want to play a wide assortment of games you will have to buy a new computer.
Upgrading from where you are will cost you more in the long run.
There are a lot of great computers out there that will cost you less than an upgrade.
Maybe you want to try to build a computer or you are an expert in computers. Well thats great but beware of the pitfalls.
I have built several regular computers but I am having serious issues with my gaming computer (Heating).
Going into gaming has been a nightmare. Sure I get awesome graphics, speed, but I pay in heat issues.
Compatibility is the worst nightmare for any computer builder. It takes serious research to build a computer today.
Just look at the posts you see here.
Of course we will help you to build any computer you want.
I would buy a workable computer so you can fool around on the internet (eMachines complete $700 or such), then dabble in the gaming world slowly by researching on building a second computer.
It might take some time but you will not be too frustrated when your gaming computer goes down when you have a workable computer.
Just a suggestion,
Let us know,
Your Hardware Guide.