I ran with scar tissue on my hammy for ~3 years. It sucked and I was never as good as I felt I should've been, but by the end of it I was running almost pain free and the only downside was that I couldn't do true speed work (no plyometrics, no flying 30s, no block starts, etc). Everything else was fair game.
Definitely start doing cardio now. Biking (if you have access to indoor bikes you can do one-legged biking), elliptical machines, and anything that doesn't put a ton of strain on the hammy will help you a lot.
Warm up thoroughly, if you feel even the slightest strain, stop before things go south. It's much easier to pull the hamstring again if you've pulled it once before, so be very careful. Start things slow.