This guide is outdated and I can no longer support it as I no longer own an HP Touchpad.
This guide is intended for users who already have a Cyanogenmod firmware dual-booting with WebOS via Moboot. I, in no way shape or form, take any credit for this. I am simply posting this as a simple, step-by-step guide on how to triple boot (as there aren't any that I have found in this section). All credits go to their respective developers. I am in no way, shape, or form anything beyond an amateur developer who happens to be an advanced Linux and Android user. Also, I cannot be held liable for any issues you may encounter while or after following this guide.
Original Arch Linux port post can be found here: http://forum.xda-developers.com/show....php?t=1364034
Obvious Bugs and Things That Don't Work
-Wifi signal is a bit weak
-Bluetooth (apparently there's a fix for this floating around one of the Ubuntu threads)
-Multi-touch (no right click :/)
-Novacom Driver (computer)
-WebOS SDK (computer)
On Your Touchpad...
-Boot into WebOS
-Connect to your computer via USB (do NOT select USB Drive mode)
-At the home screen in the "Just Type..." search bar, type the following:
-Now stop touching it and get onto your computer
On Your Computer...
-Open Novaterm (if you are running a Linux distribution, this can simply be done in a terminal by becoming root and executing the command "novaterm"
-Now let's make some terminal love!
Mount the boot directory as readable/writable:
mount -o rw,remount /boot
curl -O http://archlinuxarm.org/mirror/touchpad/uImage.ArchLinuxARM
curl -O http://archlinuxarm.org/mirror/touchpad/moboot.splash.ArchLinuxARM.tga
pkill -SIGUSR1 cryptofs
resizefat /dev/store/media 3000M
lvm.static lvresize -L -4096M /dev/store/media
lvm.static lvcreate -L 4096M -n arch-root store
mount /dev/store/arch-root linux
curl -O http://archlinuxarm.org/mirror/touchpad/ArchLinuxARM-touchpad-2011.12-alpha2.tar.gz
tar xzf ArchLinuxARM-touchpad-2011.12-alpha2.tar.gz
That's it, you're done. I advise opening a terminal once you're booted and updating the system with the "pacman -Syu" command (it definitely improves touch screen a bunch).