Training & Nutrition - Hello

Hi all,
I am a long distance runner, and I also lift weights. I decided to try biking, because running was killing my knees. I tried biking today, and i had a few questions, plz forgive me if you think these questions are dumb and obvious but I am only an amateur biker.

1. Which muscles does road biking work? mountain biking?
2. I am assuming since biking is cardio it will cut down on fat and thus give a more defined look?
3. would it give you a more defined look eveyrwhere or just in your legs?
4. I read one of the threads posted that if cardio is done too much it will start burning away your muscle? is this true? and if it is how much is too much cardio?
5. I tried running today, and I ran for an hour or 2, yet i barely sweat, when I run 4 miles in usally 30 minutes, I sweat like crazy. Am I not biking hard enough? is it the wind blowing my sweat?(lol) what do you recommend?
6. is biking good for abs?

thank you very much for your time.

-Amit

1. Quads, calves, mountain biking adds in some emphasis on arm/shoulder strength.
2. Yes it will, in my experience and I think most people's
3. Everywhere in my experience although you'll have to do other exercises for muscle in other than leg areas if you want "six pack" abs etc
4. Yes that's true, you want to avoid "overtraining" look that up and how to detect it
5. Biking is nice and breezy, and you don't get as wet as in running, neat huh?
6. No not really, the "belly breathing" you use encourages a soft stomach, you need to work your abs and back (crunches, back extensions) both for core strength and if you want nice abs.