Did you try changing some of the settings like the performance guide suggests, and the game recommends 2.2 ghz quadcore if you're using vista/7; older video cards should be left to auto-detect proper DX settings.
You could also use a background service killer that disables anything non-critical while playing BFBC2, that'll relieve a bit of stress; another issue may be overheating the video card since it's somewhat outdated (not really, but in terms of this game it is).
Try these
settings and see if it helps any:
keep window settings at whatever you're comfortable with
fullscreen=false
refresh rate=(monitor's native rate, probably 59.88899999whatever)
vsync=false
/sound/
quality=medium
voip=false
/graphics/
all low or medium (try medium first)
bloom=false (8800 isn't gonna like bloom much)
hsao=false (if it doesn't like bloom, it will commit suicide if this is true)
msaa=1
water detail=low
texture=low (change to medium if things are too "blocky")
DxVersion=auto
Fov=(between 50-65 for an 8800 GT @ a widescreen resolution, you may have to toy with this, it slightly affects performance)
That's obviously not a copy/paste list, but maybe it'll help if you haven't already done it.
I'm thinking it's more or less background services though since you're using an "old" video card and it may be overworking the pc by stressing the video card and the processor (if it's not a 2.2+ghz like the game recommends).
I can't think of anything else and i may be totally wrong, that's just stuff we tried for my brother and his is still a little sketchy in high demand situations (16+ people on screen at once) due to not being an optimal machine for the game.
I personally run with:
Evga x58 3x SLI mobo
2.6Ghz i7 processor
12 GB matching DDR3 ram
285 GTX
Even with that setup, which covers the recommended settings easily; playing at high settings with bloom on gives me a flicker occasionally graphics-wise. I'm playing in full screen though and also typically running vent, msn messenger, winamp, IE and mozilla and google Chrome in the background also; so i'm sure that's messing with it too.
In case you're looking to upgrade your machine anytime soon, mine cost exactly 3,455.78 total (US). If you have a compUSA around, they got the mobo i have for ~300, that's not too terrible of a deal, if you wanna go big grab the 4x edition and load it up with vid cards and a BA cooling system from one of eGO's sponsors; that'll usually do the trick. If you can't drop that kind of money, i'd suggest saving up for a better processor/mobo over time and then grabbing them; makes a world of difference.