Hmmm, I'm running BF with specs pretty much less than yours and I run smoooth.
Do you have cable connection? If so do you have a good upload rate? Also of course, make sure you have the latest drivers, and since your rocking a radeon, some people gain performance with older drivers, or newer ones. I've heard 3.7 have the best speed, but I persoanlly use the latest DNA drivers based on 4.1 drivers. You could also check out the MOBO options, like disable fast write, and have the AGP apeture size according to your vidcard.
Also in BF I run the res at 1024x728x32 (for some reason seems to run better than in 800x600)
Hope those pointers helped. If not check out the planetbattlefield.com forums and see if peopel are having the same issues.