CDate(Format(MyNumber, "0000-00-00"))
That will convert the number to a date, which will be displayed in whatever
format you've set as your default under Regional Settings in the Control
Panel.
If you want to force the display to be mm/dd/yyyy, regardless of what the
Short Date format has been set to in Regional Settings, use
Format(CDate(Format(MyNumber, "0000-00-00")), "mm\/dd\/yyyy")
Note that using the Format function will actually convert the date into a
string.