Your 300 is fine, it's the buggy Sony software that is giving you problems. I do not use the Sony software myself, so I really can't help you. But, be assured someone will be along soon that can. Just so you understand, you do not have to use the Sony "reader library' software. An excellent program to use instead is Calibre
http://calibre-ebook.com/ . You do need to install Adobe Digital Editions, and follow the directions to authorize your computer and your reader. You can download Adobe Digital Editions here
http://www.adobe.com/products/digitaleditions/ . Vista home is fine, I myself am using Vista Business without issues.
After getting your computer and reader authorized by Adobe Digital Editions, you can then add the books to your library in Calibre (your books will be in "my documents/my digital editions". Then plug your reader in, and add the books to it.
The process will seem strange at first, but after a few times will become second nature.
A good bookstore (better prices than Sony) is
http://www.kobobooks.com/.
At first I would suggest getting free books from this site
https://www.mobileread.com/forums/forumdisplay.php?f=126 that are ready to go for your reader. You can import them directly into Calibre without Adobe. Just download the books, import into Calibre and then add them to your reader.