Are you playing on Pokerstars 6 client or the 7 Beta? HM2 Zoom works for me on 6 and it should work on 7 beta too I've read.
Which Pokerstars region? [.com for example]
Have you upgraded to the recent beta release version of HM2? It resolves most recent Zoom problems:-
http://forums.holdemmanager.com/hm2-...om-update.html
If you are on the new beta of HM2 then the above thread is worth reading through ~ people with problems getting the HUD have usually missed something critical - firewall or other security software seem to be the biggies
Hope this helps