I know this is a dead thread, but for anybody who is looking for some info on subtitling in TCPMP it can, in fact, do subtitles fairly easily. With the latest version (0.81, not 0.72 as many people have) and the right plugins it supports subtitles - but will not work with SRT files. Instead, you simply convert your SRTs to SMI subtitles (I use Subtitle Workshop to do it) and then you can run subtitled content no problem by dumping the video and SMI file into the same folder.
Additionally, if you have an advanced container format with soft subs muxed into it (such as ogg or mkv) then using a program like virtualdub (virtualdubmod, in my case) you can pull the subtitles from one of these files and then convert using Subtitle Workshop to play these in TCPMP as well. The version of TCPMP I mentioned handles mkv's and ogg files quite well, and can even support h264 playback with a fast pda given the right codecs. They may be difficult to track down though, but I leave that as an exercise to the reader
