Biking is probably the BEST thing you could be doing, lots of road biking does wonders for knee injuries. Especially since the clip-pedals use way more hamstring on the up stroke and thus help with the quad/hammy imbalance. Usually bad knee injuries involve some joint/bone damage too, and running usually makes this worse, especially on cement. Stick to grass or softer tracks if you plan on running.
It's not worth rushing the rehab and returning to snow too early, this is a knee (and ligament hopefully) that you will have for the rest of your life. A month or two of next winter aren't worth it when you think of every other winter you plan on having.
That being said, there is light at the end of the tunnel. I blew my left ACL in 2003 and right ACL in 2005, both of them are still intact through 3 years of racing Ski Cross, stomping 50ft cliffs in the backcountry and some gnarly crashes where I swore I must've blown my knee but managed to walk away. I don't wear a brace on either knee anymore, and haven't for 3 years.
Best of luck with your recovery, and while you can't walk.. to stop from getting depressed or going crazy I used to go to the gym and bike with one leg, with the other on the handle bars in the straight leg brace. You can still do that, and some core exercises and upper body work. Exercise as we all know releases endorphins which keep you happy. Getting injured is extremely depressing, especially with longer recoveries. Also swimming is a great way to stay active, you can use the pull buoy between your legs so you're just using the upper body for laps. Hope that helps, shoot me a pm if you have any other questions on how not to lose your mind.