The instructions to install Android 2.3.5 (Pre-Alpha) on HP TouchPad have now been made available for developers by fnj00 (touch-droid community) who want to play with the system.
N.B: Normal users should not install this version as this is a pre-alpha build and some features like wifi do not work.
You can get the system dump and android.uImage at http://touch-droid.com/touch-droid.torrent or http://randomshit.dreamhosters.com/TouchPad/. This system dumps use the touch screen drivers recently made available by CyanogenMod Team.
Then you’ll have to re-partition your flash to add one partition for Android and dump the system image to the new partition.
Please visit Semi-working build of 2.3.5 on the HP TouchPad to get the step by step instructions to install Android 2.3.5 on your HP TouchPad.
After installation, you’ll have a dual boot system with Android and WebOS (default).
Alternatively, you can also watch the video below which follows the steps mentioned in the forum post above.