When Win 7 went RTM, I upgraded my laptop from XP. But to protect myself against the possibility of having data inaccessible, I got a new disk and put it in the laptop, and took the old (XP) disk and put it in a USB enclosure.
I have no trouble accessing the data on the USB drive under Windows 7. But I would like to be able to plug it in, tell the BIOS to boot from the USB drive, and be back on my old machine. The laptop is a Dell Precision M90, and it has a boot from USB option in its boot menu. But when I try to do that, it does read the drive, gets as far as putting up the Windows XP splash screen and starting the boot progress bar, and then reboots.
What do I need to do to the old disk now running on USB to allow the machine to boot from it?