By "storing a date in a text field", do you mean you're storing the string
of the date, for example, the string "3/18/2007" for March 18, 2007? If yes,
you can use the CDate function to convert the string to a real date value.
Is the date field in the same table, or in a different table? If it's in the
same table, this generic update query would work:
UPDATE YourTableName
SET YourDateField = CDate(YourTextField);