Sharon, there's a sticky in the Exercise forum that might be helpful for you:
My KNEES! I feel so old....
Boy, do I feel your pain! My years of obesity and arthritis did a number on my knees too, and I'm stalling on knee replacements (just can't deal with the idea of surgery right now

). My doctor always tells me that the best thing we can do for our knees is to strengthen the muscles that support the knee. Check out some of the exercises in that thread for ideas. Because one of my knees is worse than the other, I try to do as many single leg exercises as possible so that each leg has to work independently and the weaker leg doesn't get a free ride off the stronger leg.
Best of luck to you and your knees!