(adsbygoogle = window.adsbygoogle || []).push({}); So, you're going to need a few things before hand.
You must login or register to view this content. that's what I've got and that's what worked for me :]
Blank DVD's. For burning the gentoo iso
DVD burner and DVD burning software, whatever floats your boat on this one. I used PowerISO.
USB keyboard
USB mouse

NOTE: Gentoo LiveCD BETA v2 is approx. 620MB in size, so be prepared for the download time.

Now that you have all that, its time to get started

Step 1: Burn your Gentoo LiveCD BETA v2.ISO to a blank DVD using your burning software of your choice.

Step 2: Connect your Xbox 360 to your TV

Step 3: Make sure there is no disc in the tray and turn on the Xbox by pressing the EJECT BUTTON, NOT POWER BUTTON :]

Step 4: You will see a blue screen (no, not BSOD) with random stuff. This is where your CPU key is (FYI: to get that, combine fuse sets 3 and 5 OR 4 and 6). Once that's done and the tray is still open, put in your Gentoo LiveCD BETA v2 disc and close the tray.

Step 5: Wait... And be greeted by some penguins :]

Step 6: Set up linux as you normally would.