I exercised/ran for years w/no knee pain/not overweight. pain direct result of previous insanity/plyo. i want to run/build muscle but knees grind&hurt?

Typical with plyo: Plyometrics/insanity puts a lot of stress on your knee joints that you don't get with other exercises. I recommend running on dirt/sand-it takes more energy and is gentler on your knees. It is also common for women to have arthritis under their kneecaps due to wider hips. You may benefit from getting a gait analysis at a good shoe store since pronation (either over or under) can cause knee pain.

Water run: One way to maintain running endurance and no pressure to knees is to run at waist deep water. Find a ymca of a physical therapy pool, these aquatic running techniques allow you to maintain running, stamina, and decrease weight on your knees (plus its much more difficult). Hope this helps!