Private Sub Form_Load()
Dim i As Integer
Dim max_wid As Long

    ' See how wide the widest ComboBox entry is.
    Me.ScaleMode = vbPixels
    For i = 0 To Combo1.ListCount - 1
        If max_wid < TextWidth(Combo1.List(i)) Then
            max_wid = TextWidth(Combo1.List(i))
        End If
    Next i

    ' Set the width for the dropdown list, adding a margin.
    SendMessage Combo1.hwnd, _
        CB_SETDROPPEDWIDTH, max_wid + 10, 0

    ' Select the first choice.
    Combo1.ListIndex = 0
End Sub