Video cards are a PERT of the issue.... but not all of it. So don't get lulled into thinking JUST changing that will allow you to max out your fs2004 settings.
I have a Radeon 9800XT. When I bought it..... top of the heap.... but now "second heap"

.
But it wasn't until I upgraded the REST of the system from a 2.4gig P with a 533 fsb to a 3.2 gig Hyperthreading P with an 800 fsb that I really saw what I would consider the ability to USE the nice features in fs2004.
But I am "picky" as to getting the viauals way "up there" AND wanting a minimum of 20 fsp on short final into a big international airport with AI set at 100%.
You'll still get improved performance with a separate AGP video card........... just don't expect miracles.
best,
........john
PS: Don't waste money on an API card. If you don;t have an AGP slot....... put the money in a mobo upgrade.

Intel i7 960 quad 3.2G LGA 1366, Asus P6X58D Premium, 750W Corsair, 6 gig 1600 DDR3, Spinpoint 1TB 720