I have mesh pc with a AMD3500 cpu. 1024 of ram. NOt sure about M'board.......ASUS model but will check. Budget is not so important. Gaming requirements...CIV4 is the one in right now. Mostly they recommend a 128MB card but I am having some troubles with some games crashing so wonder if this will help. I know it's not the be all and end all and doesn't guarantee the fix but maybe it helps and it gets ready for the next gen of games?
You don't mention what card you have now so its differcult to advise something better than what you have. I agree with what Bailey08787 has said. At the end of the day the deciding factor is cost and whether you have AGP or PCI Express. I have a 7600GS with 256mb ram and it plays everything I've thrown at it at 1024 x 768 but its a middle range card. I have the same cpu as you and the same amount of memory and I am very happy with it. Heres the one I have click here if you want something a bit better click here something mega and its only worth it if your monitor will play at the highest resolution click here These are all PCI express cards, if you have AGP then perhaps this click here or a better one click here Notice I've only listed Nvidia ones as I know very little about ATI.
Now all you have to decide is how much you wish to spend, the lowest card I gave a link to the 7600GS is still a significant improvement on a 9800Pro as things have moved on quite a bit. Have a read of this click here and perhaps this to give you an idea of where the 9800 pro fits in click here . If you look at the 9800 pro and compare the same benchmark with one of the newer cards you will see what the difference is.
Sounds as though you have the same Mesh configuration as on my Mesh.
I configured what I wanted and specified a 128mb DDR FX-5500 + TV Out & DVI Graphic Card.
I subsequently found it could not cope in High Graphic mode with certain games. Earlier this year I replaced it with a GeForce 6600GT with 256MB of DDR3 Ram which I bought from Novatech for £116.90 inc VAT & Del. Excellent card, performs very well.
have a look at this refreshingly concise article from THG back in September. Gives you the best value card for a range of price points for both PCI-express and AGP flavours. I know the prices are in dollars, but you'll get the idea.