OK, as I'm familiar with Net Library (here in the States), I'll chime in ...
First, I'm not a fan of using the media center to download parts, especially with the 650 as it shows where you are in the book (ex: 2:45 along of 12:34 total). I'd prefer to tag the (long) file with "Net Library" as the title, author as "artist", and the name of the book as the (sole) track. Add a nice cover, and transfer to the reader's Music file. If you would rather use parts, you'll have to tag each separately (Part 01, etc.), and be sure that the picture is linked to each item.
My point is that Net Library mp3 books do play on 650/950's - quite well actually once you've got them set up.
By the way, the downloaded file(s) should be located in your Windows "music" area, if you are not using Mac or Linux. Tagging is easiest (recommended) via Windows Media Player; you'll likely have to tell WMP to add them.
Last edited by SeaBookGuy; 02-21-2011 at 12:42 PM.
Reason: add note