Date fields are NOT strings, they are double precision numbers. The integer part is the number of days since Dec 30, 1899 (Jet/ACE - SQL Server and Excel use different origin dates but the same concept) and the decimal is the time since midnight. Negative numbers are prior to Dec 30, 1899 That makes Dec 30, 1899 = 0.0.
So, there is no way you can store 00/00/0000. Just leave the field null. This isn't 1980's COBOL.