If you haven't read Kevin Liston's story from Friday on his adventure's hunting down rogue access points, please go read it.  I have to mention one other resource, if it comes to your area, check out the SANS Stay Sharp Program: Defeating Rogue Access Points class.  I had the opportunity to teach it in June and it does an excellent job of covering the fundamentals of how to track down these rogues in your environment.

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Jim Clausing, jclausing/at/isc.sans.org  and http://handlers.sans.org/jclausing/