Date() Function
I understand that you want to use a Date in a Query Column or in criteria row and you must be able to enter a date yourself rather than taking the System Date, right?
Use the Query Parameter option. Open a Query in design view. Select Parameters option from the Query Menu. Define a Name say myDate and select Date/time data type. Insert [myDate] where you want your date to be used.
When you open the Query in data view it will prompt for the Date and you can respond by entering a valid date in correct format like 05-25-2008.