Here's the CurrentPlaylist definition:
And here's the section for PlayFirstTrack from the IITPlaylist object:
HRESULT IiTunes::CurrentPlaylist ( [out, retval] IITPlaylist ** iPlaylist )
Returns the playlist containing the currently targeted track.
iPlaylist An IITPlaylist object corresponding to the playlist containing the currently targeted track. Will be set to NULL if there is no currently targeted playlist.
S_OK The operation was successful.
S_FALSE There is no currently targeted track, so there is no currently targeted playlist.
E_POINTER iPlaylist is NULL.
E_FAIL An unexpected error occurred.
HRESULT IITPlaylist::PlayFirstTrack ( )
Start playing the first track in this playlist.