I've had a chronic problem with calf strains over the last two years (I think seven or so separate instances). It seems like as soon as I'm finally feeling better, it happens again. It has meant that I've only been able to run about 75% of the time over that period, which has been really frustrating. I'm not sure that I have any solutions, but but here are a couple of things that I've picked up:
1. the "medicinal run" concept from the "calf heart attacks" article that Jim mentioned earlier (http://www.thestick.net/Articles/Calf_%20Heart_%20Attack.htm) seems to make a big difference in getting over calf strains more quickly.
2. I went to a well-respected orthopedist (who's a pretty serious runner and ironman triathlete as well) and his answer was that the solution is strength training and plyometrics. He sent me to a trainer that gave me a pretty extensive lower body focused workout program. The orthopedist didn't have a very high opinion of the "scar tissue buildup" theory that you see a lot on the internet for these types of injuries (i.e. that recurring calf strains are the result of scar tissue that can be broken up with some form of deep tissue massage). That said, there are lots of people who say that they have been cured that way, so I'm not sure who's right.