Rusty Russell's comprehensive User-Mode Linux HOWTO: user-mode-linux.sourceforge.net/UserModeLinux-HOWTO.html

Nagafix Ltd.'s download site, where you can obtain root filesystem images, maintained with current security patches, for a variety of Linux distributions: uml.nagafix.co.uk

The Free Operating Systems Zoo, where you can download root filesystem images for a variety of Linux distributions (and other OSes too, but remember that User-Mode Linux only supports Linux guests): www.oszoo.org/wiki/index.php/Main_Page

David Cannings' excellent article “Networking UML Using Bridging”: edeca.net/articles/bridging