Replying to Bad knees. Need help!

Hey NSers, I had some pretty nasty knee surgeries back in January and I'm still bouncing back.  I've only got about 3 months to go until ski season opens up and my goal is to get back this year!  I'm working out once and twice a day sometimes riding the bike and working on some other strengthening exercises.  Anybody have some suggestions for specific exercises I should be focusing on to get my knees well enough to ski this year?