here 
code:
var mainMessage=WMP.currentMedia.getItemInfo("title") + "  -  " + WMP.currentMedia.getItemInfo("author") + "  ---  ";
there are more tags  for getItemInfo function:
    * Author
    * AverageLevel
    * Bitrate
    * CurrentBitrate
    * Duration
    * FileSize
    * FileType
    * ID3/TMED
    * Is_Protected
    * Is_Trusted
    * IsVBR
    * MediaType
    * PeakValue
    * SourceURL
    * Title
    * type
    * WM/AlbumTitle
    * WM/AudioFileURL
    * WM/AudioSourceURL
    * WM/AuthorURL
    * WM/Genre
    * WM/GenreID
    * WM/Track
    * WM/TrackNumber