How to download videos from Nicovideo~!
This is pretty short and pretty ez. First you will need this program, NicoPlayer
(Just google it because it gets updated often and I'm not going to update the post every time;
Once you've got that downloaded, run the program. You should get a window resembling this:
Press F3. It will open up the download manager window.
(M) = video (P) = view after downloading © = comments (A) put in playlist
Here you will need to input your Nicovideo username/password, by clicking the (T) menu and selecting the first option (S).
The first screen will contain your download folder. You can leave it be and the default directory will be "Down" inside your NicoPlayer folder, or put in something custom.
Go to the tab furthest on the right and fill in your email/pass.
Now you're ready to download some shit (almost). The method you use for NicoPlayer is to copy a nicovideo link to your clipboard. So just highlight a nico link, ctrl+c, and it will pop into your download window, which looks like this:
Press yes. It should start downloading after a little while. Congratulations, you now have access to GLORIOUS NIPPON'S VIDEOS! \(≧∇≦)/
Take note that since Nicovideo has implemented their bandwidth economy scheme wherein they lower video quality across the board during Japan's prime time, this means that you will be downloading low quality VP6 Flash videos (the equivalent of low quality Youtube) instead of HQ MP4s if you choose to download at the wrong time. Also, some videos will not have an HQ download, just like Youtube.
Credit goes mostly to sekuhara for helping me understand this shit, I just compiled it into a guide. Let me know if I missed something and I'll add it in. Enjoy ~