Here is a really nice datetime calc from the MAY 2007 edition of SQL Server Magazine (www.sqlmag.com). I reprint it here because it is too good to loose, and too long to remember perfectly.
If you are reading this and don't have a subscription to the magazine, this code alone is worth the subscription. Click on the link above and... just ... do... it <smiles>
Itzik, you do good work, I love your column.
select dateadd(month,datediff(month,0,getdate()),0)
This will get the first day of the month of the passed in date (we use getdate() here). Quoting Itzik here:
The logic of this technique is a follows: Calculate the difference in terms of months between an anchor date at midnight (in this case, 0, represending the base date January 1, 1900) and the event date. Call this difference diff. Add diff months to the anchor date.