You can download ePubs from any source except B&N and Apple and load them on to your T1. Go to
www.inkmesh.com for a nice way to search across multiple bookstores for authors or titles. With a bit of extra work you can strip the DRM on books from anyplace except the Apple store and convert them to ePubs using programs such as Calibre. We don't discuss that here, but Google Apprentice Alf for the necessary tools.
I absolutely recommend Calibre for managing your library. It does an excellent job of organizing your books and loading them onto the reader. It will automatically create collections for you on your device so that series and types of books are grouped together. It's a powerful program, but easy to use. The developers update it on a weekly basis and are active in the Calibre forum.
As side notes:
The Sony Reader program is horrible and not needed on your computer if you use Calibre.
The T1 does a good job of reflowing well-formatted PDFs, but no 6" screen will do well showing technical PDFs with lots of diagrams or tables. Some PDFs just need to be seen as an entire page. If the document was scanned in as an image and not OCRed, it will not reflow on a 6" screen. If your PDFs have header and footer information, such as page numbers, journal title, etc. those will appear sprinkled oddly through the text if you don't crop them out first.