选择mysql中前一周的记录

I have data that has a date (Y-m-d H:i:s) column (the type is datetime). I'd like to select all records from 1 week before a date I enter (in the below example: 2011-09-17 00:00:00, but am having some trouble. Here's what I've got:I have data that has a date (Y-m-d H:i:s) colum