Those specs would be able to run BF2 at a good mix of medium and high settings with a resolution of your choice.
I know someone who has the same setup except his graphics card is an ATI All-in-wonder 9800 pro (which is worse than the 6600gt) and he can do the settings I said above...the game looks beautiful with them too, btw. He has very little trouble with 64 players (online) the framerate drops are usually (if any) very small and rare occurances.
Personally, your setup is very good, imo, me being one of the people who doesn't want to bust their wallet either...
I would still reccomend, as others had to make sure you have at least a gig of RAM, whether that means buying 512mb or a whole gig for you, i don't know. But, without the gig of RAM you may, or probably will not be able to run BF2 as I described earlier. I don't really know where BF2 came into this thread anyway, but I am just using it as an example.
Good luck with your system, I'd like to hear how it works out!