The Dog, and the Treadmill?

Hi. My family, and I just got a treadmill this week, and we've tried getting our 1 year old dog onto the treadmill. We managed to get her on twice, when the treadmill isn't moving. She was doing fine, just standing there, but when we hit the "Start" on, she froze not knowing what to do, so we pulled her off so she wouldn't get hurt. Does anyone know how our dog can get used to the treadmill? We really want her to get used to it during the Winter, and all because it's all cold and snowy then. And how long at the most should we leave her on there? Oh! and we will always be by her side while she is on it. Just so you guys know :-)