Improving on subtitle application

OK. In this past two months I learnt a lot on subtitles: finding them for films I had downloaded or was going to, how to add them (using Procoder) to the video files, how to correct them (moving, joining, splitting) using Workshop and then how to include them properly onto a DVD using DVDLab Pro (instead of permanently burning them).

This program has been my first incursion into proper authoring techniques, which the programs I had used till now did not allowed me to.

Now I need to still further, as this movie file I have is splitted in four-parts and I have one subtitle file. The problem is DVDLab Pro apparently demands I join each part on the program as separate films, so I may have to split the sub file too.

I anyone familiar with using subtitles on this program? Is that the way to do it?

Which other authoring programs will allow me adding the sub files as non-permanent?