problem running Parallels virtual desktop when windows and Osx already is installed

When installing my Mac book pro I used boot camp to install windows 7 so that it is bootable in both windows 7 and osx.
I am curious if it is possible to use Parallels virtual desktop software to open the windows 7 OS already installed on the Mac? In other words, I am wonder if it is possible to install virtual desktop when there already is a windows installation on the mac? I haven't been able to figure out how to proceed with the installation since it seams that the installation requires that I make a new installation of windows 7.