Law and ethics aside, you can't download it. The stream is protected.
However, you can capture it. And by "capture", I mean record it realtime, like anything else. You can play it fullscreen on the computer, then use anything you want: output to DVD recorder, use stream capture recording software on the computer, etc. Whatever you see and hear will also be on the recording, so turn off all your unneeded crap: Skype, chat, anti-virus, anything that makes noise or systray popups. Sometimes that's not easy to do.
I've read about some legal ways to download Netflix, but last I saw, that was still in the works. Maybe beta?
@sanlyn: Asking how to "backup" the rental store is against our rules, as are a few other things. But we rarely have a need to enforce anything here, as this site mostly attracts professionals and serious hobbyists, not rude/cheapskate little twits. See Forum Policies at the bottom of any page:
http://www.digitalfaq.com/forum/news...embership.html