If this is not a Bootcamp based VM (most likely): It is stored in a .pvm package (/Users/username/Documents/Parallels/), there's a file there with the extension .hdd, it's your virtual hd, the problem is that there's no direct way to access it by the OS, this is a proprietary format that might or not be supported by other vm apps, VMWare Fusion supports it, hence my suggestion.
If it is Bootcamp based, just boot your mac into Windows.
Last edited: May 25, 2012