Slug-firmware enables you to download Debian installer images with the proprietary Intel ethernet driver already included. Once downloaded, check the file integrity with md5sum.
To flash our Slug, you have various alternatives, depending on what OS you run and what firmware you are upgrading from. I used upslug2. Martin's detailed all alternatives.
The Debian installation is pretty straight forward, just a bit long as the Slug is not that fast... and depending on your internet connection speed also. once you're set up, you can use your Slug like any Debian server...apt-get install wahteveryoulike... Just keep in mind that the resources of your slug are not unlimited !
Take a look at some cool applications I run on my Slug.