The code looks like this:

In your General Declarations:
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
(all of the above is one really long line)

In the sub where the MIDI will be launched:

'ret = mciSendString("open PATHNAME type sequencer alias myfile", 0&, 0, 0)
ret = mciSendString("play myfile wait", 0&, 0, 0)
ret = mciSendString("close myfile", 0&, 0, 0)
(where I typed PATHNAME, replace it with the full pathname or default path to your Midi file, e.g. c:\midis\xxx.mid)
That's all