http://www.zoly.info/kindle-app-for-pc/
I have the kindle app on my PC. I also have the kindle app on my iPod touch. I would like to move a free kindle sample book that I downloaded onto my PC to my iPod Touch. I would also like to move another free book that I downloaded to my kindle iPod app, to my PC.
When you download something from the Kindle store, it is automatically backed up on your Amazon account, and you can put it on any device with a Kindle app. I believe all you have to do is download it again from Amazon on your iPod. And if these are free books, there’s no harm in downloading it again, anyway. They’re free. (: Kindle App for PC

Sync kindle for PC with kindle for iPod Touch?