I had a lot of problems on multiplayer until I did this:

Go to Start, Run, type in msconfig.
Click on Selective Startup, then unclick load startup items (I think that's what it says....I'm on my laptop now and it doesn't have that option)
Click ok
Restart PC

This will kill all programs that start up automatically when your pc is started......I had lots of problems on multiplayer before I tried this, now I rarely have a problem.

Mike