Now it's time to install the kernel.
The easiest way would be to pull an already prepared binary kernel; there are packages for some distributions (currently only Mandrake and Debian) or a source package, and rebuild it on your system.
If for some reason you cannot use them or have problems using them you can also build your own kernel with the bruby patch, for more information how to do this visit the Backstreet Ruby page on building and installing the kernel: http://startx.times.lv (or some of the mirrors) -> Documentation -> Quick Kernel.
(If you are new to Linux, reading "The Linux Kernel HOWTO", http://tldp.org/HOWTO/Kernel-HOWTO.html, could be very helpful.)
You can find binary kernel package for Mandrake-9.1 at http://varna.demon.co.uk/~svetlio/ruby-contrib/kernel.html.
Debian binary kernel packages are available at http://www.schuldei.org/debian/bruby, or as apt repository "deb http://www.schuldei.org/debian/bruby ./ "