Open a snapshot recordset, sorted on the field you are interested in.

Get the .RecordCount value:
 if it's an even number
   get the n/2 and n/2 +1 'th records and use the mean value

 else if it's an odd number
   get the (n+1)/2 'th value and use that

 else
   there are no records in the recordset

 end if

There is example code around on the web -- I think Steve Lebans has some on
<http://www.lebans.com>

Hope that helps

Tim F

Here's a function I use...

It works just like the included domain functions...

Public Function DMedian(Expr As String, Domain As String, Optional Criteria
As String) As Double
Dim db As DAO.Database
Dim rs As DAO.Recordset
Dim Temp As Double
Dim OrderedSQL As String

'construct SQL
OrderedSQL = "SELECT " & Expr
OrderedSQL = OrderedSQL & " FROM " & Domain
If Criteria <> "" Then
   OrderedSQL = OrderedSQL & " WHERE " & Criteria
End If
OrderedSQL = OrderedSQL & " ORDER BY " & Expr & ";"

Set db = CurrentDb
Set rs = db.OpenRecordset(OrderedSQL)

rs.MoveLast
NumRecords = rs.RecordCount
rs.MoveFirst
rs.Move Int(NumRecords / 2)
Temp = rs.Fields(Expr)

If NumRecords / 2 = Int(NumRecords / 2) Then

   'there is an even number of records
   rs.MovePrevious
   Temp = Temp + rs.Fields(Expr)
   DMedian = Temp / 2

Else

   'there is an odd number of records
   DMedian = Temp

End If

rs.Close
db.Close

End Function

HTH
Sam