I personally think cardio is pretty important. Not only for the cardiovasuclar benefits, but also because I just feel like I really worked when I am finished. Have you tried like the olyptical glider? These are low impact, and not real hard. Also, I have to have music when I am doing cardio, it is imperative. I like to use a mix of songs I like, usually aligned in a certain order so that I get one that really pumps me up (hard rock, or whatever) during the tougher portions of my run. I know that I start to struggle right around the half way point, which is at the 15 minute mark, so I put in a pumping song at that point on the cd. (use cd burner, etc.) Seems to help me a lot.

-Chris