I have gotten a number of requests for information about this, both here on ZDNet and through other sources. In the interest of not posting a lot of technical details here which are probably not of interest to all that many people, and hopefully making the information more widely available to others who are interested in it, I am in the process of adding detailed instructions to the Linux Laptop Wiki. So far I have added instructions for Ubuntu 8.04 LTS (Hardy Heron) and 8.10 (Intrepid Ibex) to the HP 2133 page. I will be adding instructions for 9.04 Alpha 6 (Jaunty Jackalope) later today.
Update: As of now, 15:00 13/3/2009, I have added the Ubuntu 9.04 instructions. They are based on the Alpha 6 release, which just came out.