simple Kudos thread!
You can mark an SD partition active by following: http://www.kozio.com/blog/how-do-i-make-an-sd-card-partition-active-under-windows-7
I had to hold down the S2 (USER/BOOT) button near the microSD card, while applying power to the board (by plugging in USB cable) in order to boot this firmware and extract the eMMC image. Pressing RESET while holding the S2 button did not work. After several seconds, I released the S2 button and then the LEDs started blinking. It seems the boot sequence doesn't proceed while S2 is being held down.
Edit: A further test shows that holding the S2 button for too long (15+ seconds) causes the board to turn off.
Note: I just formatted the card with FAT32 and copied the files to it. I did NOT mark the partition as 'active', but DID have to hold down the S2 button when applying power.
Wish I'd noticed all these comments earlier. When in doubt, you might drop a note to http://beagleboard.org/discuss.