When I was a regular runner in my teens and twenties, I used to suffer from runner's knee and had to keep taking breaks. In my breaks, I swam like crazy to keep in shape.
Now, looking back, I can see that I did so much wrong. I ran as much as possible, as often as possible, did not cross train, did not weight train and took as little rest as possible. I always ran on pavement (sidewalk) or road. Hmmm.....what's wrong with this picture?!!!!!
I would go to runnersworld.com and start reading up on running and how to do it properly. Some people are lucky and can run without stopping, suffering few injuries and regularly abusing their body without any retribution from their body. I wasn't one of those people, sounds like you aren't either!
So, while I agree with Kathryn and I too am a dedicated power walker these days, this year, I have begun running again, because I miss it, and there's nothing quite like it. But, I now do it differently because I love my knees, we have a fabulous relationship and I want us to be together forever. Know what I mean?!!
You may not have to give up running, but you will need to adjust your approach and your thinking.
You do not need to run more than 3 times per week to enjoy all the fat-loss and endorphin high of running. You can make great progress in endurance and technique with just 3 running workouts per week. The book, "Run less, run faster" by Bill Pierce and published by Runner's World describes this type of training and the successes you can expect with it.
I only run three times per week, no more, and I see great results in increasing speed, endurance and stress relief.
On the days when you don't run, you cross train, but with cardio activities that do not add high impact to the joints and knees. Here's where your power walking, swimming, cycling, etc, comes in. Not high impact Cathe cardio. You also weight train, including specific exercises to target the hamstrings (running tightens them, they need to be lengthened and stretched out during cross training activities), quads, and tendons and ligaments that surround the knee. The quads are the muscles which protect the knee, so keeping them strong (and keeping a balance in stregth between the quads and the hamstrings) helps your patella to move with correct alignment, thus cutting down on injury.
The other major change I have made is I run exclusively on a treadmill, thus reducing the impact that resounds through the body with every step. So far, I have had no pangs of anything from the knees, fingers crossed.
Check out your sneakers too. Pain and injury are often signs that the shock absorption of our running sneakers is gone and it's time to invest in some new ones. Go to a good running specialty shop so you cvan be fitted properly with the right type of sneakers for your foot and strike type. Runnersworld.com has more info on this too. read up, OK? A good running store also can point you in the direction of good specialists who can analyse your strike and foot and see if you need to correct the bio-mechanics of your running stride, or whether you need custom made orthotics.
If you love running, try some or all of these adjustments before resigning yourself to a life without running.
Hope this helps,
Clare