I can get the internet versions to read Quick Help and Manual but cannot find how to download these so that they can be accessed from the Audacity Help menu without the need to be online. OS is Linux Mint 12 on one computer and Ubuntu 10,04 on the other.
Personally I’ve set up a folder on the “Bookmarks Toolbar” of my web browser (Firefox) and have several bookmarks in that folder to a number of pages in the manual, and some pages in the Audacity wiki. As the Audacity help is in HTML format and displays in the web browser, I find that this method is just as convenient, but more flexible than using the built-in help.
However, to answer your question, the instructions for installing are here: http://manual.audacityteam.org/man/Unzipping_the_Manual
Note that the location of the manual after unzipping is crucial. If you Audacity does not see the manual after you have installed it, please say if you installed Audacity from the distribution repository (for example through the Software Center) or by some other means. Also, please state the exact location of the file “index.html” in the help.