I'm wondering if its possible to set up parallels with administrator rights in advance for the mounting and unmounting of the bootcamp partition? It gets rather annoying to type and retype the password as windows reboots every once in a while.
I've seen some discussion of altering OSX config files to prevent it from mounting the bootcamp partition on boot, so that Parallels will not have to unmount + remount the volume when it uses it. My searches turned up nothing though, so i can't remember the specifics or if it was successful (I think it wasn't though.) Try some searches on the forums, but it may just be something to live with for now.