This code prevent the use, in a Combobox, of any keys except the Return, Tab, and Up and Down Arrow Keys:
Code:
Private Sub ComboBoxName_KeyDown(KeyCode As Integer, Shift As Integer)
Select Case KeyCode
Case vbKeyReturn, vbKeyTab, vbKeyUp, vbKeyDown
KeyCode = KeyCode 'Accept these keys for Combobox usage
Case Else
KeyCode = 0 'Block all other keys
End Select
End Sub
Just replace ComboBoxName with the actual name of your Combobox.