Since day one, the HP TouchPad hasn't been treated very well by its parent company, and as always, it's been up to the hacker community to save the day. Last month, Google open-sourced Android 4.1 (Jelly Bean) for third-party modification. As such, nobody should be surprised to learn TouchPad owners can now install Jelly Bean on their tablet (albeit it's currently a CyanogenMod 10 build).
Over on XDA Developers, forum user "Jcsullins" has revealed an Unofficial CM10 Preview based on Google's latest mobile OS. HP probably doesn't care, but anyone who knows that their HP TouchPad will never get a proper OS update is likely jumping for joy. This build currently only has partial hardware video and graphics acceleration. Furthermore, audio isn't working, and there is no front-facing camera or microphone support. Still, it's definitely a start.
It is now my job to give you the usual warnings. If you're not feeling confident, don't bother doing it. Stick with whatever you currently have on your HP TouchPad, either webOS or whatever flavor of Android (2.3 or 4.0) you've put on it.
Some users are reporting their device doesn't charge properly after installing this pre-release CyanogenMod 10 build, but this isn't happening for everyone. Personally I would recommend waiting a bit longer for this one, assuming you use your HP TouchPad on a regular basis. If you just want to hack around and have some fun, then by all means.
With all that out of the way, the download links you need are as follows: CyanogenMod 10 ROM for the HP TouchPad and the latest gApps package if you want Gmail, Google Maps, and other Google apps. For detailed instructions on how to install this build, check out RootzWiki.