If you own a Kindle 1/2/DX or an iPhone/iPod Touch, then mobidedrm.py can strip the DRM from Kindle AZW ebooks. The Kindle also has a a small percentage of its ebooks in TOPAZ format, which is locked to Kindles. There is now Kindle for PC, so anyone (in the US) can buy Kindle ebooks but currently mobidedrm does not work on K4PC ebooks.
We don't know how easy (or not) it will be to strip the DRM from B&N ePubs. It is possible today to buy eReader ebooks from B&N, and strip their DRM with ereader2html.py.
Once an ebook, of almost any kind, is DRM-free, Calibre can format shift it to LRF or ePub for the PRS-600.