The key is to find an exercise that works for you and won't cost a lot of money or preparation time.
Jogging is free -- except for the shoes -- and you can get started now. Maybe just a long walk the first time out is the way to go.
Completerunning.com has a list of 100 tips that range from motivational (buy running clothes that look good) to the practical (do not increase your mileage more than 10 percent per week) to funny (give horses wide berths on trails and walk as you pass them unless you enjoy a hoof to the melon).
Yoga is another easy way to get started. Many health clubs offer classes, but you can get started in the comfort of your own home by buying a DVD or checking out moves at Prevention.com, has an in-depth article covering everything you would ever need to know about getting started on home yoga.