If you have to de-sub the entire video, the only way that isn't going to drive you completely insane is just cropping.
If it's just a scene or two, and you're
lucky, you might be able to overlay the beggining of the scene (when the sub hasn't popped up yet) on top of the subbing. This only works if the scene isn't moving where the subs are.
And yeah, for the rest of the stuff (which is a pain in the ass, for the most part) check out
the guides.