Hello Tony,
The Date Question type should be avoided, this field is great for Birthdate, Credit Card Expiration dates, etc..
But I would recommend that you make this a Question Type = Textbox. You can even include a jQuery Datepicker to allow the user to select a date from a great looking calendar. You'll see this plugin here:
http://jqueryui.com/datepicker/ The same SQL Validation you have above should work with a Question Type = Textbox.
Please let me know if you have any questions.
Thanks,
Ryan