I don;t have either card but I've seen a lot of posts written about this subject, and this is a summary of what I can tell you from them:

Both GREAT cards - very fast. The Radeon 9700 is equipped to cope with the new features of DX 9 where the GeForce isn't. This won't make any difference in FS2002 but it should in FS-COF. How much is anyone's guess at this stage.

The other factor is the forthcoming GeForceFX cards (also DX9 fully enabled) . They should be roughly on a par if not better than the 9700, and will result in the 4600TI taking a nosedive in price shortly.

Depends how much you have to spend and how big an improvement the new DX9 effects will produce. If they're really good, you should obviously opt for a Radeon 9700 or the GeForce FX. If they aren't, (and no-one's seen them yet), you may well be throwing away big dollars on a marginal visual improvement.

Be careful here - you need to check which Raydeon card they're fitting.

There are several in the Pro series. Anything less than the 9700 and you'll still be getting a good card, but not to the specification I gave above.

buy the radeon. with that card, you're able to play the newest games of the next year with high details. if you do not want to pay so much money ,then buy either the 9700 or 9500pro. they also got a very good performance (both faster than the 4600).
the geforce fx ain't that good. it's faster than the 9700pro, but it's more expensive, too heavy (pay attention when transporting the pc - the card may break your AGP-slot) ,and too noisy.