you may find the following info useful:
Apple's Macbook Air Developer Note:
http://developer.apple.com/legacy/mac/library/documentation/HardwareDrivers/Conceptual/MacBookAir_0801/Articles/ProductDeveloperNote.html
Macbook Air Hacking USB Ports
http://www.maushammer.com/systems/mba/USB.html
it seems the South Bridge chip in the MBA supports several USB ports that aren't wired to anything...
have fun