Shopping around for a new form of exercise you can do indoors now that the leaves are turning? Might I suggest spinning? If you have never tried a spin class you might want to know what to expect before climbing up on a spinning bike and taking your heart rate for a wild ride.
Spinning is a potent form of cardio exercise and you can burn upwards of 400 calories in one class (that is why it seems like one of the favorite exercise forms on The Biggest Loser). You ride a stationary bike designed especially for spinning surrounded by motivating music and an instructor leading you through a workout. Some spinning instructors will give you lovely images as they tell you to crank the resistance on your bike for a "climb up a steep and beautiful mountainside." The instructions vary as will your pace and sometimes you pedal as fast as you possibly can; other times your goal will just be to keep your bottom off the bike seat. Essentially you will climb, sprint, and cruise to build your cardiovascular endurance. Plus it is a nonimpact exercise so it won't jar your joints the way running might.
If you are heading to class don't forget to take a couple of towels because you are going to sweat buckets. And with that in mind, don't forget your water bottle. Also make sure to adjust your seat to fit you so your knees are slightly bent at the bottom of your pedal stroke.
To read about the downsides of spinning, check out Spinning 101.
Fit's Tips: As with all exercise classes, you are ultimately in control. If you need to alter the instructions to make it through the class go ahead and decrease the tension. I also strongly suggest introducing yourself to the instructor prior to class and outing yourself as a newbie.