source list in iTunes 7?
The Audiobooks source list in the iTunes 7 LIBRARY source group appears to use the same criteria for what is an audiobook as the iPod. So, tracks which are in Audible.com’s .aa format or in Apple’s .m4b Protected AAC format should appear in the Audiobooks source list, as long as their bit rate is 64 kbps or lower. (Bit rates higher than 64 kbps don’t make sense for audiobooks, it doesn’t improve their quality noticeably.) The easiest way to change the format is explained in the prior answer.