Found two problems...
Firstly I have to put the filename of the font in, "FRADMCN.TTF".
Secondly the forum software appears to have put a space in between the "subtitle" and "(". Removing this space and changing the filename looks to have fixed it - I ran a quick test from frames 10 to 300 and "Going somewhere, Solo?" appeared over the Lucasfilm logo.
So the subtitle filter is working anyway...
Can I just check something? Are you using the PAL or NTSC DVDs as a source? If you're using NTSC then it's possible the frame numbers may need changing for the PAL version...