I just got MacBook Pro 2011 and installed Windows 7 using Boot Camp.
I am a Windows user who need to develop iOS apps.
Is it possible to install Mac OS VM on Windows that is installed using Boot Camp?
There are various (hacky) ways to do this
But I would urge you to install VirtualBox in Mac OS X and then install Windows on that. You can run Windows full screen. It's going to be very quick and allow you the best of both worlds.
Best of all VirtualBox is free and available here http://www.virtualbox.org/