I suffered re current pulls in both legs a couple of years back. You'll receive some excellent advice from the physios on here. Mine were alleviated by prolonged stretching prior to a run. they both seem fine now.
In reply to kingjam: I feel your pain matey, I've been having similar since pulling it 4 months ago. Mine is right behind the knee, so the physio I use has been concentrating in that area but also IT band and top end calf which was really painful.
Lots of stretching regularly and I'm getting better, although its still there in the background.