I am having the same problem, getting the session lost message on low ping servers (150ms or less). Â I have:
AMD Athlon 1900, 512MB Ram, GF3 ti500 graphics card, Windows XP, Cable Modem (Comcast) 1500up/256down, tried all Speedguide and DSLReports tweaks, RWIN at 37960, MTU 1500
All drivers are current, and I have no connection problems with other online games. Â I have tried all the the suggested crashing/freezing fixes but they haven't worked.
I am using a Linksys Router also. Â Tried bypassing it and plugging the computer directly into the modem with no results.
Another thing I noticed is that it I can usually play 1 or 2 maps in a row ok, but get booted at the briefing stage for the 3rd map.
Also, I seem to be losing more and more memory with each MP map played like this:
  Boot up     389MB
  Start OFP   264
  Second map  193
  Third map   99
I've shut down everything I don't need running and the game is still eating up alot of memory. Â Using memory optimizers like Cacheman and Clearmem, but still crashing.