madshaun1984 haxnetworks favourite moderator (after me of course ) has made the tutorial he promised. This is all his work, so don't be misguided by lamer sites stealing his work and passing it off as theirs.

Here is part of his tutorial:
You will need a usb keyboard and mouse for this install.

First off decide wether you want to install on a usb hdd or the ps3's internal hdd (internal hdd will need to be formatted and a partition assigned to OtherOS).

Then get a copy of the OtherOS.bld for petitboot and put it on a usb stick at /PS3/OTHEROS/otheros.bld

Burn yourself a copy of the ubuntu desktop 10.04 ps3 .iso from the ubuntu site.

Once done goto system settings/install OtherOS, and insert your usb stick with the OtherOS.bld on it in the ps3.

Here is the crucial point if installing on a usb hdd, when prompted about the otheros partition being formatted, just say no, and proceed to install otheros without formatting your ps3's hdd (Or if you want to install onto the ps3's hdd, you can say yes to this step and follow the instructions).

Once the otheros.bld is installed, say no to rebooting to otheros and remove the usb stick from the ps3, insert a usb hdd, and the usb keyboard and mouse now, then goto system settings/default os and select otheros, then reboot to otheros when prompted or reboot the ps3 via a shutdown and pressing the power button.