What graphics card can I buy?

[ddubois]

I have a Gigabyte GA-K8NS Ultra-939 motherboard, a AMD Athlon 64 3200 939 CPU, a 1 gig of RAM, and two 2100fp Dell monitors. My graphcis card is a dated ATI All-In-Wonder (AGP) who's extra TV features I gave up on. I mostly web browse and poker, but I also game some, and I want to buy Civ 4, which I hear is a hog. (Also, I'd like to be able to run two sessions of EQ simultaneously on each monitor, but any EQ window I move to the second monitor has atrocious performance. I heard this might be an ATI Hydravision problem, which would be another impetus to ditch my current card.)

I want to buy a new graphics card, one that will last me as long as possible, but I wanted to first check with you guys to make sure I don't buy 'too much' graphics card for my system (in other words, I don't want to spend $500 and find out my card is half-wasted because I'm CPU bound or whatever).

Any advice appreciated, thanks.