RTR,
Without knowing your budget it's hard to make a reccomendation.
That said, the best PCI card out is:
POWERCOLOR ATI RADEON 9200 Video Card, 256MB DDR, 128-bit, DVI/TV Out, PCI, Model "R92P-D3L" -RETAIL
Model# R92P-D3L
Item # N82E16814131237
Specifications:
Chipset/Core Speed: ATI RADEON 9200/250MHz
Memory/Effective Speed: 256MB DDR/400MHz
BUS: PCI
Ports: VGA Out(15 Pin D-Sub)+TV-Out(S-Video)+DVI connector
Support 3D API: DirectX®8.1, OpenGL®1.3
Cable/Accessories: Not Specified
Max Resolution@32bit Color: 2048X1536@60Hz
Retail Box (See pics for details)
Note this not a 9200 SE, Its a 9200.
$98 at Newegg.
I have a Celeron 1.4, 384 RAM, with a FX-5200 Ultra. It works great in AHII with the performance sliders in the middle. It's an AGP card only as far as I can tell.
Adding more system RAM would help, but only a little. Your main problem is your video card.
I think your system will work fine with this PCI card and maybe 256 more ram. Total cost $175.
However if you have more than $200, forget the PCI video card and get a new MOBO that has a AGP slot, re-use your Celeron 2.6, get 512 of RAM, and a $150 to $200 vid card. I saw Frys has the ATI 9800 Pro for $199 this weekend, it's an awesome card for that price. An Asus MOBO is about $74, the RAM $85, = Total $350.
In the future you can always replace your Celeron with a P4 in this MOBO.