User Guide for Wireshark 1.2.11

If you are working on a Windows PC, then by default, the user guide is located in "C:Program FilesWiresharkuser-guide.chm". If it's not there, you can get it by following a few steps:

1. Visit http://anonsvn.wireshark.org/viewvc/releases/ to find the subversion revision number and date associated with the release you are interested in. In your case, 1.2.11 corresponded to subversion revision 34021 and was released 3 months ago on August 30, 2010. (REF: http://www.wireshark.org/news/20100830.html)
2. Visit http://anonsvn.wireshark.org/wireshark-win32-libs/tags/ and look for the tag date that is closest to, but not after, the release date. In your case, this is tag 2010-08-27-1.2/
3. Navigate to the packages/ directory and download the user-guide-#####.zip file you see there. In your case, this is user-guide-31672.zip. Don't worry that the subversion revision number attached to the file doesn't match the subversion revision number associated with the file. That simply means that the user guide probably wasn't updated since that revision.
4. After downloading the file and extracting it, you will have the user-guide.chm file corresponding to your desired release.

I don't know where or if the pdf renditions of the user guide are archived.