Replacing adding subtitles

[gr0bda]

I tried search and kind of can't find a guide that would suit me. It was either how to add permanent subs or how to rip from dvd and add to other formats etc. And software was always different, way more than I'd like to download try to learn all it's functions and test all day long as to what would suit me.
I'm looking for a guide that will help me:
1. convert subtitles files in my native language made for divx .txt (I think) to dvd format.
2. Let me add my own subtitles even if subtitles were previously stripped
3. How to find what file is the subtitle file? Is it .ifo? .sub? (I checked both and they conatin tons of info, but no movie dialogs) Oh, and if there are multiple ifo, sub or whatever files, would I have to check each and everyone or is there a quick way to figure out which one is the subtitle file?
4. How to replace existing subtitles. Say if menu points to spanish subtitles and I'd click on spanish, but they would be replaced by my own and I'd get my own language (I don't care if it wouldn't look very estetic. I just want it done quick and efficient)
TIA

[gr0bda]

Well I learned on my own how to rip bitmap subtitles off a dvd using SubRip. But now I don't know how to insert my own.

What I'm trying to do is to replace French subtitles with my language. I know how to rip it, but now, how to replace it? And on top of that how to convert from txt to bmp and then replace it... help?

[gr0bda]

I got DVDs (original mind you) of Matilda and Rambo II. Both of them got only spanish subtitles (WHY!?!?) (and maybe french too. Don't remember.)
I wanna rip'em to HD and:
1. Add another SELECTABLE language (it doesn't have to be in menus, just as long as I can change it on the remote)
2. Replace spanish subtitles with my own language.

I got Subtitles in english (srt) and my own language (txt)

HOW!?
Someone help? Point me to a guide, nothing more!