rar support for squishee is coming (I didn't add it because the 7z command in the p7zip package for OS2007 is broken -- p7zip-7z package for OS2008 should extract rar from the command line -- have you tested?).

The next version (0.2) will poll the system for known archive extraction tools (tar, zip/unzip, unrar, 7z etc) and will offer a tree view of the archive contents. I'll probably save archive creation and selective extraction for v0.3

If you want rar support in squishee now, make sure you install p7zip-7z then, as root, either
1. hack the squishee.py script in /usr/bin and change the command invocation string from "7za x ..." to "7z x ..."
2. create a symlink from 7z to 7za: ln -s /usr/bin/7z /usr/bin/7za (make sure you don't have p7zip-7za installed)