Thanks, gr8npwrfl. Thing is, I couldn't format the SD card when it's loaded with the Jetbook, because the SD couldn't be accessed, even though a drive letter was given to the SD card.
I think I might have found a workaround. I transferred an ebook to the SD card with a cardreader, and then inserted the SD card back into the Jetbook. Now when I reconnected the JB to the PC, I was able to access both the Jetbook drive and the SD drive!
Very strange! So glad it worked.