maybe try to recompile the kernel by hand. the best way to do that is to use Gentoo, but they are prepathcing the kernel before put it in the repository. i think you can do this with any other distro.

after that read the code of some modules and try to find bugss or howto abuse them. but be sure that the kernel is not written from newbie programmers.

am not so advanced. it would be interesting to hear the opiniion of the gurus.

Gentoo is a good place to start if you want to learn about the kernel. You can also do recompiles in other systems. I would recommend doing a few customizations before you go hacking away at the source code.

First, visit www.kernel.org and www.tldp.org for useful how-tos and other kernel documentation.

Next, don't give up on running your experimental OS in a virtual machine. I have done a fair amount of kernel development for both Linux and Solaris with VirtualBox VM's. The important thing here is that the host needs to be a stable system - I use CentOS/RHEL 5 as my host (8 cores and 8gb ram) and run newer Linux clients (Gentoo, Ubuntu, et al) as well as Windows and Solaris x86 as guests.

Actually, in Gentoo, you can get a kernel.org kernel without any patches.
There are a variety of kernel packages available. Here are 3:

To use the kernel patched by Gentoo:

emerge gentoo-sources

To use the latest released kernel from kernel.org

emerge vanilla-sources

Or, to use the daily git snapshot from git.kernel.org

emerge git-sources

http://www.gentoo.org/doc/en/gentoo-kernel.xml

Or, as with any distro, you can just download the tarball from kernel.org and have fun. Gentoo (potentially) makes it easier because it is required to compile the kernel yourself anyway.

In addition, make sure that you know what areas of the kernel you want to hack at. Honing your focus will help a ton. The kernel is a big piece of code!

I would take a look at GoboLinux. GoboLinux uses a kernel patch to hide the traditional filehierarchy's structure. Something that is rather simple like this would be a great start.

You may also want to look at some projects online such as Linux ABI and Longene.