Lots of the people on this site use various exercise machines. I use a stationary bike myself, and I know at least a couple use a treadmill. Any exercise at all is great for weight loss, but only if you do it enough.
"Enough" varies from person to person, but you should find a level that a) you can maintain for at least 20 minutes at a time, and b) makes you actually sweat! Once you find that level, you should work your way up from it, either in terms of time, or difficulty, or even better, both. You should also exercise at least three times a week, and the more often you do it, the better!
Also, its generally recommended that you see your doctor before starting exercise regimes, especially if you have any preexisting conditions.