+1 1saxman and Mondoman.

Ease into biking gently. Have a local bike store (LBS) set up your bike for the commute now with tires, and wheels if you need them. Then learn to keep it clean, oil it, fix flats, and so on, until you are doing complete overhauls.

Also, if your bike is "older" and of unknown quality, ask the LBS if your bike is worth fixing. A big box store bike may not be worth the cost of wheels and tires.