Replying to New Skier, Bad Knee, Any Suggestions?

Went skiing for the first time last year and absolutely loved it!  Bought my first set of skis, and I'm ready to hit the mountain this winter.  The only problem is that I had knee joint surgery 3 years ago, and I have some lingering pain and instability.  Has anyone had a similar problem and how did you deal with it?  Any suggestions for how I should get started? I would like to hit the park as much as the mountain.  Is a knee brace a good idea?