Date format of yyyy-mm-dd for field entry in user form

Hi, I was wondering if there is a setting for textbox in a user form to ensure that only the following format is entered.

yyyy-mm-dd can it be done through "tag" option?

also somehow my today() switch from 2012-09-23 to 23-09-2012 even though the default in excel is set to date canda format.

maybe a vba code I can set when I open the workbook to ensure it is set properly?

Any guidance greatly appreciated.

Anne