What kind of bike is required for the spinning DVD? We have a cheap stationery bike, can you use that? Or do you need certain features to use it? I've never worked out in a gym (have worked out to Cathe and other exercise DVDs for the past 20 years!) so I don't know what a spinning class is or what is required! What kind of bike is needed? Trying to decide whether to order it in pre-order or not. Will Cathe recommend a bike to get?