If you have a support contract you can go to their support site: http://support.openview.hp.com/
...then go to Downloads > Software Patches and look up the QC version and platform that applies to you to see all the patches released. For Windows, it looks like the most recent publicly released patch is SP2 (a.k.a. patch 4). However, HP generates patches almost every month and just doesn't publicly advertise them. They may have patch 6 on hand, but only give it to people who ask for it because they need it (have a configuration that requires it).
(Opinions and information contained in this post are wholly my own and do not reflect the opinions of my employer.)