Does Apple's license for OS X allow it to be virtualized on an HP PC?
Lion is the first Mac OS X to license some virtualization on the non-server OS.

From the 10.7 EULA:


(iii) to install, use and run up to two (2) additional copies or instances of the Apple Software within virtual operating system environments on each Mac Computer you own or control that is already running the Apple Software.


Notice the condition, though: it's only allowed on Mac hardware when running Lion as the host OS.  There are also provisions for installing it over Snow Leopard macs. 

Running it on HP hardware would likely be a violation of the license as written. Check with your lawyer as always when the question of legality is involved since any license has to respect your local laws.