Auto-Completar Combobox

Vamos desde o principio, primeiro cole o seguinte código em um módulo

Option Explicit
Private Const CB_FINDSTRING As Long = &H14C
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
Public Function Combo_AutoCompletar(xCombo As ComboBox, ByVal xKeyAscii As Long, Optional ByVal xUpperCase As Boolean = True) As Long
    Dim lngFind As Long, intPos As Long, intLength As Long, tStr As String
    With xCombo
        If xKeyAscii = 8 Then
            If .SelStart = 0 Then _
               Exit Function
            .SelStart = .SelStart - 1
            .SelLength = Len(.Text)
            .SelText = vbNullString
        Else
            intPos = .SelStart
            tStr = .Text
            .SelText = IIf(xUpperCase, _
                           UCase$(Chr$(xKeyAscii)), _
                           LCase$(Chr$(xKeyAscii)))
        End If
        lngFind = SendMessage(.hwnd, CB_FINDSTRING, 0, ByVal .Text)
        If lngFind = -1 Then
            .Text = tStr
            .SelStart = intPos
            .SelLength = (Len(.Text) - intPos)
            Combo_AutoCompletar = xKeyAscii
        Else
            intPos = .SelStart
            intLength = Len(.List(lngFind)) - Len(.Text)
            .SelText = .SelText & Right$(.List(lngFind), intLength)
            .SelStart = intPos
            .SelLength = intLength
        End If
    End With
End Function

Agora no Form use o seu código:

Private Sub cboNome_KeyPress(KeyAscii As Integer)
KeyAscii = Combo_AutoCompletar(cboNome, KeyAscii)
End Sub

assim tem de funcionar