This isn't a very elegant solution, but I think it works.
First, set the default value of your date field to Now().
Then, in the On Current event of your form, enter the following (in the example, the date field is called flddate)
Private Sub Form_Current()
Dim MyDate, MyWeekDay
MyDate = Me!flddate
MyWeekDay = WeekDay(MyDate)
If MyWeekDay = 1 Then
Me!flddate = (Me!flddate + 4)
ElseIf MyWeekDay = 2 Then
Me!flddate = (Me!flddate + 3)
ElseIf MyWeekDay = 3 Then
Me!flddate = (Me!flddate + 2)
ElseIf MyWeekDay = 4 Then
Me!flddate = (Me!flddate + 1)
ElseIf MyWeekDay = 6 Then
Me!flddate = (Me!flddate - 1)
ElseIf MyWeekDay = 7 Then
Me!flddate = (Me!flddate - 2)
Else
Exit Sub
End If
End Sub
HTH
Chris