What I did was gut my old computer and get upgradeable new parts and slowly upgrade everything. Your socket is old so get a new mobo, processor, and vid card (I have an X700 PRO and it runs every game I've thrown at it, even FEAR), and make sure the ram is compatible, e.g. DDR or DDR2, for that reason and the gaming, try to go with AMD.
Try a socket 939 mobo. Since your computer is an older one you can stick with the DDR standard and your current RAM should be backwards compatible (not fo sho, but pretty sure, I haven't dealt with AMD-based chipsets much, but like AMD's performance in gaming) so you can upgrade that in the future.
When you get the money in the future, you can get cheap value RAM for about $90-$100 a Gig. Check my sig, it's not the fastest, but it gets the job done.
P.S. Don't feel bad about owning a celeron, I got one too. But right now I'm waiting on a new mobo to throw in a pentium d 820. But I want an AMD bad!