Three weeks out with a calf injury (again!)

Calf injury occurred on Dechmont 10K Training Run on 29/9/11.  That's three weeks with almost no running.  Overuse has caused my left calf to tighten, thus preventing me from running and now I have re-injured it on three separate occasions.  As of today I've now missed three races that I had pre-paid.  My focus now is the 2012 London Marathon.  Slow return to running is now my only option - missing it so bad!