Stop thinking about it and do it.  Start riding a bike to work tomorrow.  It will help increase your fitness, burn extra calories, and save you a few parking tickets.  It’s a fun way to be environmentally friendly too.  Start by parking a half mile from work.  Then each week back up another half a mile until you can leave from home.  Bike into work one morning, catch a ride home from a friend, offer to drive to work the next morning, and then bike home to make sure you stay committed to adding to your cardio.