Sasage, up graded both of my video cards a couple of months ago with the Gainward TI4200. Cards are excellent. I run Flight Simulator2002 and the graphics are great. Don't forget to up grade your video drivers too.
92 Bonnie SE aquired on 7-1-03 with only 88K miles.
Dell Dimension 8200 2.4 ghz
768mb PC800 rdram
Gainward 64mb GF4 TI4200 Ultra/650 golden sample video card
Win XP SP1
Don't get the FX. They aren't built as well as the GeForce 4. For value, the MX440 or 400 is fine. I got one for 50 bucks for PCI, so I'm sure it will only be a bit more for AGP.
My friend has an ATI 9000, and he hates it, and I see him having problems with it all the time. It'* the drivers.
NVidia cards are nicer with drivers, so you will be pleased with a MX 400 or whatever. Or, do what aviator said and get the Gainward 4200. They make great cards. I have a Gainward 4800 and it performs better than most cards out there.