Here's an interesting page from a translated version of the Al Qaeda training manual. This section discusses methods of communication between members. It *doesn't* mention steganography, though it does say things like, when talking on the phone,
] "Conversation should be coded or in general terms so as
] not to alert the person monitoring "
For those who prefer a PDF version, there's one at the DOJ site here: http://www.usdoj.gov/ag/manualpart1_2.pdf