I've started writing this exercices a long time ago (something like ~1 year), I wanted to see what a kernel overflow looks like and how you can manage to obtain an elevated shell.
Currently, (only) 3 "levels" are available, each one show you a different type of flaw.
Actually, it's pretty simple ; first, you have to setup a Windows (XP, VISTA, 7) virtual machine thanks to VMware/Virtualbox. Then, you register the differents drivers with the administrator account and you create a 'key.txt' in your documents (your goal will be to read this file with a limited account). Finally, you create a limited account, you try to elevate your privileges. If you succeed at this job, you will be able to read your secret key.txt file !
You can find the solution I've made in the solution/ directory ; theoretically those exploits work on winxp/vista/7 -- if they don't feel free to reach me by email/irc/twitter/whatever.
I hope you will enjoy those little exercises ; but if one day you have a nice idea for a new level I'll be very happy to add it :).