I did my first day of Insanity yesterday and it was much harder than I remember. My plan is to do the workouts five days a week instead of the recommended six. I want to give myself some more rest days since I am running, swimming, biking, and boxing throughout the week also. I am going to go another Insanity tape tonight, in addition to a swim and a 2 mile run. I am pretty sore today but I love that feeling. My hamstrings, calfs, and back are sore, which may make working out tonight pretty difficult but I am going to try anyway.
Also, I am looking into buying some running shoes that will help keep my knees from hurting. I over pronate when I run so I am looking at getting some Nike Lunarglides :)