Most subtitles are textbased and can e.g. be edited in Notebook.
Further, there are editors like the one I use (mainly to synchronize, but you can e.g. also edit displaytimes with it, or e.g. change format from .smi to .srt), i.e. Vladimir's "Subsync"
http://users.pandora.be/vlad/subsync/index.htm (it covers Sami, SubRib and MicroDVD subtitle files or .smi, .srt and .sub files)
Another program for this purpose, covering more subtitle formats perhaps is (I personally have no experience with it, as I dont use it):
http://viplay.cs-wuzz.com/english/pa...leworkshop.htm