Plus one on that. I used to dual boot but found I couldn't install SP1 or custom themes etc onto Windows. GRUB gets in the way. So now I installed Ubuntu 11.04 on it's own drive with my other two drives disconnected.
Now, if I just switch on the machine will boot Ubuntu, GRUB takes over.
However, if I press F12 I get a one time boot choice. So I can boot the Ubuntu drive or the Windows ones.
This seems a much simpler way of doing it and so far so good