There are a bunch of tools for reading CHM (Microsoft compiled help files) on Ubuntu-Linux.
A number of them are listed on the site http://www.ubuntugeek.com/how-to-view-chm-microsoft-compiled-html-help-files-in-ubuntu.html
I have tried a number of them but I like xCHM one as it keeps the tree navigation easier.
The whole installation stuff is clearly listed on the given link.