i've never tried doing hardsubs, but softsubs are ultra easy (and preferable to most). I use gknot, make sure i have vobsub installed (sometimes i have to reinstall the vobsub decoder from gknot to get it to register though), and then follow the guide over at
http://www.doom9.org .
Basically, go to the subtitle tab, click the first button, load up your .ifo file. select the language your after/remove unwanted one, if it's a one cd movie, rar up the srt file, and rename the archive and idx, if it's 2cd cut it with the next button in gknot (using virtual dub to get the length of the avi for the chop), then archive and rename the subs.
ie.
movie.avi
movie.idx
movie.rar
or
movie.cd1.avi
movie.cd1.idx
movie.cd1.rar
movie.cd2.avi
movie.cd2.idx
movie.cd2.rar
srt files can play from inside an archive and this will save u lots of space (make sure u have the right .idx though)