lngItemIndex = SendMessage(cboIn.hwnd, CB_FINDSTRING, - 1 &, ByVal strFindString)

Option Explicit
Private Const CB_FINDSTRING = &H14C
Private Const CB_SHOWDROPDOWN = &H14F
Private Const LB_FINDSTRING = &H18F
Private Const CB_ERR = (- 1 )

Private Declare Function SendMessage Lib _
    "user32" Alias "SendMessageA" (ByVal _
    hwnd As Long, ByVal wMsg As Long, _
    ByVal wParam As Long, lParam As Any) _
    As Long

Private Sub Form_Load()
    Combo1.AddItem "French fries"
    Combo1.AddItem "Hamburgers"
    Combo1.AddItem "Milkshakes"
    Combo1.AddItem "Onion rings"
    Combo1.AddItem "Ice"
    Combo1.AddItem "Ice cream"
End Sub

Private Sub Combo1_GotFocus()
    SendMessage Combo1.hwnd, CB_SHOWDROPDOWN,  1 , ByVal  0 &
End Sub

Private Sub Combo1_KeyPress(KeyAscii As Integer)

    Dim CB As Long
    Dim FindString As String
    
    If KeyAscii <  32  Or KeyAscii >  127  Then Exit Sub
    
    If Combo1.SelLength =  0  Then
        FindString = Combo1.Text & Chr$(KeyAscii)
    Else
        FindString = Left$(Combo1.Text, Combo1.SelStart) & Chr$(KeyAscii)
    End If
    
    SendMessage Combo1.hwnd, CB_SHOWDROPDOWN,  1 , ByVal  0 &

    CB = SendMessage(Combo1.hwnd, CB_FINDSTRING, - 1 , ByVal FindString)
    
    If CB <> CB_ERR Then
        Combo1.ListIndex = CB
        Combo1.SelStart = Len(FindString)
        Combo1.SelLength = Len(Combo1.Text) - Combo1.SelStart
    End If
    
    KeyAscii =  0 
    
End Sub