Don't forget library books! I know those are not "purchases", but if you have or can get a library card for a library that offers ebooks you will be able to read those on your PE too!
There's good info in the MobileRead Wiki (very top of page) about libraries (and ebookstores) if your local library doesn't lend ebooks.
The fine points of how to get books into your PE and into the Library of your PE are discussed in The Welcome Basket, courtesy of Borisb, on the enTourage forum as well as in many posts there. You will find the videos and User Guide on your new PE helpful as well. And if you're stuck -- well, you've already found who/how to ask!!
Enjoy!!
