Wait wait...your wording is very sketchy, do you mean lag as in bad FPS or as in ping. Everyone knows ping is mainly affected by your ISP, thats not the issue were talking about here. Were talking about FPS performance with your card, which should be very bad. I say this not to diss your card ( heck even my x800 is getting old and senile ) but to let other people know the truth. So someone doesn't rush out there with an x550 expecting optimal performance in BF2 when truth be told, they will get very dismal performance. I'd say around 10 FPS if you max the settings.
Originally you stated your card can max out settings without any lag, you refered to lag as in FPS lag, not ping/latency lag which you now claim what you originally ment. Your not making any sense, and frankly i don't think your worth the time.
BTW I suggest you get a 8800 GTS for 250 after MIR instead of the 8600 as the 8800 GTS performance is LIGHT years ahead of the 8600.