Re: breathing problems
The BIGGEST mistake people make when starting to ride a bike is trying to push the pedals in a gear that is too hard. The object of riding a bike is NOT to give your legs a workout, it's to give your heart a workout. You should use a gear which will allow you to spin the pedals as quickly as possible while still making reasonable forward progress.
For most people with a mountain bike, the should mean that the chain is on the middle ring in the front (where the pedals are attached... your indicator should be on the number 2) and somewhere near the middle of the "cluster" in the back (where the wheel is attached... again, somewhere around "3" or "4" if you have seven speeds).
from Philly, dude.