A couple of years ago I dislocated my knee and damaged my patella tendon. Not as seriously as you it just stretched rather than tearing but it took the NHS a little while to get there act together about assessing and treating it so I had 3 weeks of doing nothing and the muscles in my leg wasted away to almost nothing.
In Aberdeen there is quite a good NHS physio team, they gave me a heaps of exercises to do to help strengthen my leg. Most of these involved a resistance band (a massive elasticated band) that was used in various ways to build specific muscles to help strengthen the knee. They also put me on weekly sessions on a ultra sonic machine thing (yes that is its technical name as far as I am concerned) which was to help break up the build up of scar tissue.
I would really advise against trying to run on you knee as the repetitive shock forces of running are really bad for recovery. Once you have got the full range of motion of your knee back I was advised cycling was a good exercise for it as it is low impact.
Basically my advice would be try and see a physio, as SBZ says any good physio should be able to give you a detailed program of exercises to aid recovery. If you are in the UK your GP should be able to refer you to one, if you have any private medical insurance through your company or maybe a bank account use it to get some.
Good luck with your recovery.