As far as I can tell, there's no OS X CHM reader, so the only way to view the contents is by decompiling the CHM with chmdump. It's available as source code only, but it compiles without a hitch on 10.2. Compiling is simple:
- Download the file
- Extract it
- Open Terminal.app and cd to the chmtools folder
- Type make
And that's it. You may want to put the resulting chmdump file into a folder in your path. (I put it in /usr/local/bin.)
To decompile a CHM, type chmdump {CHM file} {destination folder}. There will be a bunch of files the Help Viewer uses for searching and indexing. Ignore those and look for a folder of HTML documents. You can then view the HTML files in your browser.

