Ryan,
My MBPro has a 320gb drive, half for win7, half for osx. I would say dual boot is safer than parallels, but I have used both (VMWare, not parallels, but the same sort of thing.)
It boots up to Windows by default as I prefer windows, unless I am editing with FCP, of course.
As Walter says, its always best to be as clean as possible with an edit system, but I have a Mac desktop for more serious editing and have had no problems running windows on a mac.
Mark.