In the words of Abrasive. I just ordered mashed up the answers to my questions also into it for clarity.
High probability that these tablets come with uboot as their bootloader.
There are two ways of doing this - tell uboot to boot linux from the SD-card or install linux on the flash.
The easiest route is to start by booting from SD, then move everything into flash. However your main problem would be the fact that the only input device on a tablet is a touch-screen and debian installer doesn't support touch-screens as of this writing.