I currently own a Macbook Pro, and got rid of the optical drive to instead use a second hard drive in its place.
This second hard drive contains an installation of Windows 7, which was installed from my Mac using Boot Camp. (So it's actually a 10GB partition of Snow Leopard, and a 290GB partition of Windows 7.)
Booting into Windows 7 when this drive is installed in the normal hard drive bay functions properly. When I move the second drive to the optical bay, it no longer boots. (Though the Mac OS X partition boots fine.)
My question: My Windows knowledge is fairly rusty - is there a known limitation that prevents Windows from booting from an external disk? (I'm seemingly also unable to boot into the Windows install CD from an external USB CD enclosure that now contains the optical drive.)
Edit: I should mention that I have rEFIt installed on the laptop, so both partitions appear at startup, but upon selecting the Windows partition, I get the dreaded blinking cursor. (With no error message.)