How to view chm file and open rar file on Linux

For chm file, you can use following package:
gnochm, kchmviewer, xchm. You can use apt-get to install those package. On CentOS, you can use DAG repository: http://dag.wieers.com/rpm/FAQ.php#B1
to install.
For rar file, use unrar package.

Ref:
http://www.cyberciti.biz/faq/open-chm-file-under-linuxfreebsd/
http://linuxondesktop.blogspot.com/2008/02/viewing-chm-files-in-linux-with.html
http://www.mydigitallife.info/2008/07/08/how-to-open-and-view-or-extract-chm-compiled-html-files-in-linux/