;-) If you hold down both mouse buttons at boot, you can access an early start menu that will allow you to boot from any mounted bootable drive, without regard to priority. Of course, you'll have to do this every time you boot.
The software used to format your hard drive will also allow you to set each partition's priority, I seem to recall. You could theoretically set HD0: to a priority lower than DF1:'s -10.
Mind you, make sure you back everything up first, just in case.
