You can find weatherproof demarc boxes here:
»www.hometech.com/hts/pro ··· erproof/
While you can prewire, most cable companies won't just connect at the street end and leave it at that. They'll want to hook up every outlet you want, test them, and possibly charge you for it.--
If it's important, back it up... twice. Even 99.999% availability isn't enough sometimes.