Try this:
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
Private Sub cmdTrayOut_Click()
x = mciSendString("set CDAudio door open", 0&, 0, 0)
End Sub
Private Sub cmdTrayIn_Click()
x = mciSendString("set CDAudio door closed", 0&, 0, 0)
End Sub