Swimming is great. too.

I had a treadmill that I used religiously for 6 weeks before it got dusty. lol. Quizzickle's advice is spot on. The only thing I can add is that once I got up to 15/20/30 mins, I made sure I had music or a little portable TV in the room to help keep me from getting bored. The scenery doesn't change much when you're walking on a treadmill.