>IMHO, index on date field (SQL Server 2008) or index on datetime field is all you need. I don't think you need to use any integer conversions, unless you build facts table.

Well, one thing for sure, whenever I remove a date field as part of my where clause, this is much faster. I have found the following sequence:

1. Integer, Boolean and Character fields (Faster)
2. Add a date field such as StartDate greater than something (Slower)
3. Add the same date field such as StartDate greater than something AND StartDate less than something (Even slower)