USB booting :: Boot from MMC

Hi,

I'm trying to boot DSL from my MMC-card. My bios allows booting from USB and other removable drives.
I installed bootusb-0.8.img on my USB and it worked perfectly. Now I want to boot DSL from my MMC-card, and yes u guess, it won't work. I try it with and without the bootusb-0.8.img on my card.

What I've to do?

Thanks in forward

original here.