Windows On Mac :: Installing Win7 64-bit / Screen Stays Entirely Gray

I'm trying to set up Windows 7 Home Premium 64-bit on my Mac mini (bought in April 2009). When I use VirtualBox on Mac OS X, I have absolutely no problem installing Windows 7 64-bit in a new virtual machine. However, I want to run it Windows 7 natively on my Mac mini. So when I insert the Windows 7 DVD and reboot my Mac, holding the C key down so as to boot from DVD, then it does seem to be reading the DVD, but all I get is a light gray screen. I then hit the Return key, and it does seem to do even more. Still the screen stays entirely gray.

I have the impression that it behaves like it does with VirtualBox, except the screen stays gray all the time. When I use VirtualBox, the first thing that happens is that it prints "Hit any key to boot from CD or DVD" (or something like that). When I do hit a key (e.g. Return), then it continues printing "Setup is loading" (or similar) and loads more stuff from the DVD for about 90 seconds. So it really seems to be that it does just that when using it natively (without VirtualBox), just the screen stays gray.