Pete, I will repost and concur with what mister multipath said in a previous post;
For those of you looking for OmniPeek Personal... It isn't licensed for use in any corporate environment. By using it in those environments you are breaking the EULA. Also OmniPeek Personal is old and does not have 802.11n decoding capabilities. Anyone interested in OmniPeek should go to their website and request a trial of the latest version and then convince your boss to purchase the product. I actually use 4 different WLAN sniffers: Fluke's AirMagnet, Omnipeek, Tamosoft's CommView for WiFi and of course WireShark.
Personally I mainly use AirMagnet and occasionally AirPcap. I'm afraid most of the free one's are kind of limited so its worth downloading trials until you find one you like to work with. My company has standardized on AirMagnet WiFi Analyzer and I think for the money its really worth it. I've used BackTrack a fair bit as its got so much more to it than just analysis tools. Its a great tool as well. Good luck!