We have received full embed permission from NicoNico Douga, which I believe is a first for an English language anime site, and perhaps for a solely English language site too.
With this you can freely post and view videos from Nico without an account or otherwise.
Posting is simply a matter of placing the URL of the video in your post, just as with YouTube and similar.
So paste "http://www.nucovideo.jp/watch/sm2321776" in to get the following:
There are two essential stipulations to using videos from Nico in your posts:
1. Please do not post any videos from Nico alongside (in the same thread as) ero or guro content. This violates the terms of our agreement, so we will have to remove any such errant videos.
2. Please do not ask anyone involved with Sankaku Complex in an official capacity how to download videos from Nico. We will have no choice but to ignore any such questions.
Other usage notes:
The videos will be affected by the dreaded economy mode as usual; typically this runs from 1900-0200 JST (GMT +9), and depending on the video (especially popular ones) may result in dramatically reduced visual quality.
You can get round this by buying a NicoNico Douga premium membership (500JPY a month) - this will ensure full quality at all times both on Sankaku Complex and on Nico.
Commenting and other such functions are only possible whilst logged in, and from the Nico site itself - just click the window as usual to go to the relevant page.
The interface to the external player should be simple enough - the icon in the bottom right corner will turn off comments.
You can feel free to post you favourite videos in this topic to test.