psw to student visa

hello everyone,
the story is that I am on PSW visa at the minute after doing Masters degree from a university and my visa expires in 2.5 months. i was thinking about switching to entrepreneur visa but i am not too sure if its worth it or not.

i am also thinking about switching to a student visa and planning to do a PHD. but want to clarify if you can still work for 20 hours a week on student visa or not because i found out through "someone" that students will not be allowed to work at all after June 2012. can someone please throw some more light on this?

Your quick response will be highly appreciated.