To access Adobe DRM protected books (like Overboard from your library), you will need at least Adobe Digital Editions. You can install it from:
http://www.adobe.com/products/digita...?promoid=DNRHZ
This Adobe package is reliable, easy to install, and has it's own EBook Reader for the PC.
The Sony software would install this, and the only other thing you need the Sony software for is to access the Sony store. Not a big loss.
For library management it is hard to beat Calibre.
Robert