Concerning NicoNico Choruses...

So, let's say you hear this absolutely amazing chorus on Youtube, and you just HAVE to download the MP3 to put it on your iPod. I've been there and I can relate, lemme tell ya. But wait! You don't want to download it from Youtube, oh no - getting to the original video and downloading THAT MP3 is what you want. How might one go about this? Well, if the original NND (NicoNicoDouga) link is in the Youtube video's description, just click the link that will be one of two kinds:
http://www.nicovideo.jp/watch/sm--------
This would be an mp4 video. You can tell by the letters (here, they're 'sm') before the 8 dashes, which will be 8 numbers for an actual video, much like Youtube's /watch?v= system, but without letters.
The other kind is this:
http://www.nicovideo.jp/watch/nm--------
This type of video is an SWF. Again, you can tell by the letters (here, they're 'nm') before the 8 dashes, which will, again, be a sequence of 8 numbers unique to that video.
So you just copy the whole URL or just the sm-------- or nm-------- and go to this site. Paste the address into the yellowish box that says 'ニコニコ動画のURLを入力して、MP3へ変換♪', and then click the light blue button that says 'MP3（｀・ω・´）変換'. It should take you to a page that looks similar to this page. If it gives a box that has a heading of some Japanese text and and red 'error!' message, you either didn't copy the right URL, you didn't copy the whole thing, or the video is protected under copyrights and you need to get the MP3 another way, such as downloading the video via the NicoFox FireFox addon and converting it to MP3 or maybe something else entirely.

But what if the link to the original video isn't in the description???
Easy fix, as long as the title of the video is still in Japanese and not translated. You just copy the title and go to this site (the first link I mentioned in the previous paragraph). In the upper right should be a search bar that says Googleカスタム検索, which means 'Google custom search', as in, search this site using Google. So nice of the admins!
So, take the title you copied earlier and pop it in the search box. If any of the results are completely, or almost completely bold, that's what you're looking for, so congratulations!
If they aren't bold... I'm sorry, I can't help you. >.<

But what if you don't want to download the song? What if you really, really liked a picture used to represent one of the singers, but don't know how to find that picture? The Japanese tend to be very considerate and copyright-aware, they wouldn't use the picture without giving credit where credit is due, would they?
No, of course not!
But it's not like there are a bunch of Piapro (like a Japanese DeviantART) links in the video's description, so where would those pesky links be hiding, anyways?

I'm gonna use the 【*15人合唱*】千本桜-和風Band Edition-【*7人合奏*】 video as an example.
Basically, this is the translation of the description:

Maro "Sound-source-responsible mallory here (´◕ω◕｀)"
Min " Video-responsible asaki here （* ◕ a ◕ *）"
Maromin "Together we are Maromin!"

This is an arrangement of various things. It's very poor quality, please use your browser's back button OTL

(For the following names, the titles are omitted)
❀ Original tune / Senbonzakura (Thousands of Cherry Trees) → sm15630734　✿Japanese style Band Edition karaoke → sm16143369　❁Sound source / pictures → mylist/28813886

(Singers)
Kakichou, Gurutamin, Kouhei, Konii, Shiren, Touyu, Bibi,
Fujikura, Mafumafu, Mitani Nana, mokaleph, Yuuto, ytr, Reji

(Instrumentalists)
Gibuson, Tomohachi, Yaffui, Mokona Wing, 530, Sakuya

(People in charge)
Maro: Personnel selection / Karaoke production / Part division / MIX / Avatar selection / Scraps mylist/9640252
Min: Avatar selection / Raw materials production / Video / Encode mylist/23242639
-------------------------------------------------------------------------------------------
So after looking through all the listed videos and Mylist's, I couldn't for the life of me figure out where the HECK the pictures were!
But the Japanese, being the technologically genius people they are, integrated into NND an amazing feature:
On the Mylist pages, what I thought were the descriptions under the titles of the videos were in reality the, shall we say, comments, of the author of the Mylist. In other words, it's like the Mylist author's very own description box for the video, in addition to the original video-maker's description - the one that you see when viewing the actual video!
After realizing this, I clicked the Mylist where the sound sources and pictures apparently were. Sure enough, in each singer's description box on the Mylist page was the name of the singer and the link to the picture used for them!
Needless to say, I now have a very sexy pic of Kaito.
Me gusta. X3

A couple tutorials

Though the second post already leads to one of the tutorials, there's a page of 6 or 7 tutorials, all related to NND. It can be found here. There's also 2 tutorials on what 歌ってみた are from the 'usual' approach and the 'anime' approach.
By the way, I WILL be making posts that don't just link to other posts, I'm just trying to start this off here...>.<

The Lingo

Just like English has a bunch of slang words and phrases (ftw, lol, lmao, omg, etc.), Japanese does, as well. By no means am I going to attempt to teach Japanese on here (if you really want to learn, and you prefer that it be online, I strongly suggest going here), but I'll at least give you a rough idea of what the comments are all about. I think a good place to start learning about them is here. Another good post by the same person about live broadcasts on NND can be found here.
Have fun! ^.^

Registering

I think that to start this blog off, registering would be a good first step. When it comes to YouTube, you don't need to be signed in to watch videos, but on NND, you can't watch them without an account. Therefore, here is a link to get you started. I didn't make the post on the link, so don't give me credit, please! Enjoy!