1) video format is a proprietory format :-( - not standard Mpeg. You may want to check out
http://www.cruftbox.com/cruft/docs/tivoextraction.html2) I have successfully added a 160GB hard drive to my series II 40 gb model. I bought a NON-transferable lifetime Tivo subscription $300, which has now paid for itself over the month to month fee). But if I messed up my Tivo's install, and it couldn't have been repaired (NON-warranty, of course), I'd lose the subscription as well. Point is that I was on pins and needles during the upgrade, for fear of messing things up.
The directions are NOT drop dead easy - perhaps to one who has already hacked a TiVo before, reminds me of linux man files - they sure make sense if you already understand it! There were overlapping instructions (if you have this kind of Tivo, do THIS, otherwise do THAT) and questions which were only answered by reading the thing completely backwards and forwards like 20 times. The instructions, of course, make PERFECT sense ONCE YOU'RE DONE. Piercing the virgin experience was less than comfortable.
3) Short of completely hacking out your TiVo (and there are websites which discuss this like
http://www.tivofaq.com/hack/ ) I would suggest you getting a cheap PC, check out one of those *MPEG* Haugpauge video cards (down to $60 now - not a simple TV capture card, it encodes mpeg realtime) and using:
http://www.mythtv.org/edited for technical info