In your condition, a 23-mile roundtrip commute should be a piece of cake. That doesn't mean it won't take some getting use to, however. Your aerobic fitness isn't the issue, but your comfort level riding on a bike, adjusting to the saddle, and using different muscle groups. For some excellent advice for a new bike commuter, see this thread:

http://www.bikeforums.net/showthread...-New-Commuters

If you don't have a bike, I would recommend visiting local bike shops if that's in your budget. Proper fit is essential on bikes -- probably the most important issue for new riders -- and a good bike shop should be able to recommend the right size for you. It might cost more money in the short run, but will probably save you money in the long run and make it more likely that you will continue riding. If you already have a good idea about what size bike fits you, then you might want to shop for used bikes on Craiglist or other local venues. You can often find very good values on used bikes but it's easy to buy something that doesn't fit if you don't have a good handle on that.