I have to third Jeff's "store dates as dates" recommendation. I seem to spend a lot of time trying to convince people of this. Some people like to store some date parts differently or make up their own approach. Once you get bitten by doing this, you'll convert and stay converted. Your data will then follow. 🙂

One word of caution, however, is that the datetime data type is a point in time, not a duration of time. I've seen where people get in trouble trying to store a duration as a datetime data type.