Courtesy of http://www.delphifaq.com/faq/f614.shtml

Private Declare Function mciSendString Lib "winmm.dll" _
  Alias "mciSendStringA" ( _
    ByVal lpstrCommand As String, _
    ByVal lpstrReturnString As String, _
    ByVal uReturnLength As Long, _
    ByVal hwndCallback As Long) _
  As Long

Public Sub cmdOpenCD_Click()
Dim lRet As Long, returnstring As String
    lRet = mciSendString("set CDAudio door open", returnstring, 127, 0)
End Sub

Public Sub cmdCloseCD_Click()
Dim lRet As Long, returnstring As String
    lRet = mciSendString("set CDAudio door closed", returnstring, 127, 0)
End Sub