The only thing I can think of is: the field you write to in the table is of type numeric. It's impossible to write leading zero's to a numeric field. Access probably translates your input (from a form?) to a valid long integer.
Do you have access to the table? If so, check the field type. change it to 'text'. If it's OK that you store these numbers as text with a leading zero.
Good luck, Bart Verlaan.