You can take a look at these sites.  Maybe they will help.

http://j-walk.com/ss/excel/files/xdate.htm

http://support.microsoft.com/kb/214058

Hi,
Excel doesn't handle dates prior to 1900. When you enter such a date in a
sheet, eg. 1/1/1600, it is entered as text (left aligned while regular dates
are right aligned).
On the other hand , vba and MS Access handles dates prior to 1900.

-You could either keep your data in an MS Access table and query from excel.
- or you could wrap the regular vba functions into vba to make it a UDF
useable in a sheet. Eg regular vba DateDiff --> DateDiff2 for the sheet:
Public Function DateDiff2( _
   Interval As Variant, Date1 As Variant, Date2 As Variant) As Variant
  Dim d1 As Date, d2 As Date
 
  On Error Resume Next
  d1 = CDate(Date1)
  d2 = CDate(Date2)
  If Err <> 0 Then ''' error converting dates
     DateDiff2 = CVErr(xlErrValue)
  Else
     DateDiff2 = DateDiff(Interval, d1, d2)
     If Err <> 0 Then ''' error for Interval
        DateDiff2 = CVErr(xlErrValue)
     End If
  End If
End Function

DateDiff2 works llike vba DataDiff, but it can also be used in the sheet, eg:
   =DateDiff("m",A1,A2)
--> returns the number of months between dates in A1 and A2. Even if these
dates are in the 1600s and therefore understaood as Text by excel, when
passed to the function , they are converted to regular dates and the
computation can then work.