Wow!
Thank you very much, Don!
To tell the truth, i got a PRS-500 reader, bought from one of the forum members a month ago (thanks Will!)... but it's faulty too, and it seems almost impossible to fix (bad nand flash). I think it will be easier to fix a button (if it's just that) than trying to understand how to flash a nand from U-Boot (i already did the hardest part: soldering and building a working UART cable).
I'll let you all know how everything goes with Xerxes' Cybook.
Once again, thank you, Don!
Lazaro.