Hi everybody,
I'd like to suggest wsusoffline. It's a pair of scripts with a GUI for configuration.
The first script downloads microsoft security updates for various of their products (different Windows and Office versions) and saves them on a CD, DVD or a portable device.
The second script automatically detects the appropriate updates for the machine it is run on and installs those.
The products website is
http://www.wsusoffline.net/
The product is both open source and under GNU GPL.
It is already portable in the sense that it only stores and modifies files in its installation directory.