I need to find all the records that were last modified more than one month ago, and delete them. How do I create the date dynamically with MS SQL?

dateadd(month, -1, current_timestamp)

To see it in action run this:

select dateadd(month, -1, current_timestamp)

For more information, see the MS docs: http://msdn.microsoft.com/en-us/library/ms186819.aspx