According to eHow, there's a script that converts .EBK into HTML (Win, I guess). From there, you can convert the HTML to your preferred format.
http://www.ehow.com/how_5829336_convert-_ebk-_pdf.html
There's also a .EBK reader software for Win:
http://www.nauticalmind.com/EBK-eBoo...-pr-81495.html