I just finished playing BF2 for awhile, and I'm running with an Intel 2915 a/b/g wireless card and a Netgear WGU624 router. I use the 5Ghz "a" band. It's hard to tell if it's the server or my network that's making BF2 a bit laggy, but since I always play on full 64 player servers, it's probably BF2. My speed drops sometimes, and I'm trying to resolve the issue. It doesn't seem to impact actual internet speed, since the slowest it has dropped to is 6mbps, which is more than my 5mbps internet connection.
Currently, I believe that the problem is caused by the wireless card in my laptop, which is less powerful than my router. While the computer can pick up the router fine, it may be that my wireless card can't transmit a powerful enough signal sometimes.