For some reason, I keep coming back to this thread, so I must have something to say. I seem to have a sympathetic reaction to your problem, Kalvin00.
The first thing you need is to properly identify your board, there's a whole family of ca810's with varying capabilities. Use these links-
810
810E
With that info, you'll be able to plan ahead.
I really don't understand why folks are trying to convince you that you need a whole lot of expensive new stuff to radically improve game play. Your $$ and family situation seem pretty clear to me, and your original concept is quite sound. Yeh, the agp bus is superior for graphics, but it's not a night and day difference between that and the pci bus, not at your relatively modest desires. Your onboard graphics are easily the worst of relatively late model solutions, even a GF2MX or Radeon 7000 pci would be a radical improvement, and the radeon 7500 is at the top of the reasonable solutions, all things considered. When your processor becomes the bottleneck, that will be at a much higher level of performance than you have now. If it turns out that your board is one of the late 810e's, you have some potent and inexpensive cpu upgrades available as well...
So, uhh, don't give up- keep checking the for sale/ trade forums, might get a good deal on an upgrade card, maybe a 1gig celeron if your board will handle it...