Had been trying to figure this out for the last 2 days. Finally got it I can turn on/off subtitles.

The TCPMP player and subtitles add-on must be of the same version. I am using 0.72RC1. Install the player, then the add-on. You may need to soft reset to get it to work. Start the program "TCMPMP Subtitle Edition". You must then change the player's default Video Driver from "Intel 2700G Decoder" to "Intel 2700G" or a few others for the subtitles to show. Open the movie file. The .smi subtitle files shold have the same name and located in the same directory.

P.S. If using DVD Decrypter, you have to extract the subtitles from the VOB files to a seperate file using a tool like freeware "Subrip". Or perhaps you can extract the subtitles from the divx file as well. Then change the subtitle file into .smi format.