When you first boot OpenDarwin 7.2.1 (x86) I found that on Virtual PC,
I have to hit enter to get to the boot prompt, and then manually
specify the boot device. The format of this command is:

• rd=disk0s1 -v

Now the specific device might vary on your installation so you’ll have
to possible put different values for the channel and device (e.g.
disk#s#). The ‘-v’ is the switch for verbose mode.

After completing an installation, you can go and edit the preferences
file:

• /Library/Preferences/SystemConfiguration/com.apple.Boot.plist

Look for the ‘Kernel Flags’ key tag and enter the same string that you used above (e.g.
rd=disk0s1) within the string tags following it. This will set your default boot device.