I knew I was pushing it, and 4 days in a row of cardio (2 on the elliptical and 2 on the treadmill) have made for some sore knees today. What really sealed the deal is that I did the C25K workout on Sunday instead of the power-walk. So today, I stuck with the actual plan and completed the Day 5 strength and interval walk while watching a season 2 episode of Dawson's Creek. It wasn't too bad until I got up to 4.5 and 5mph. Then my knees were a little unhappy.
I'm definitely going to need to play tomorrow's workout by ear. This constant cardio may not be in the cards.