I run the Aircrack-NG VMware image available from http://www.aircrack-ng.org/ with a Belkin USB Wireless adapter similar to the one here: http://www.belkin.com/au/IWCatProduc...duct_Id=182815 (Sorry I am not in the office to give you the exact model I am using) and it works great.

The VMware image allows me to move across physical systems and set up the environment for my staff/colleagues and I found it dead easy to set up and use.

Once you have it all set up and working I have found the following tutorial on the Aircrack site quite good to give new people a bit of an understanding of the possibilities.
http://www.aircrack-ng.org/doku.php?id=simple_wep_crack

There are better tools depending on what type of auditing you are actually doing (i.e. rogue access point detection/location versus wireless cracking versus wireless enumeration versus sniffing) but this in easy way to set up a simple cracking and enumeration auditing tool

cabby80