This video by pkerry12 will show you how to install windows 7 via bootcamp on you macbook air with just USB flash drive. To install [highlight]Windows 8[/highlight]  follow the exact same processes. Just replace Windows 7 ISO to Windows 8 ISO image.

Windows 8 Release Preview ISO images

http://windows.microsoft.com/en-US/windows-8/iso

Windows 7 USB download utility link
http://images2.store.microsoft.com/prod/clustera/framework/w7udt/1.0/en-us/Wi…

rEFIt link for mac
http://refit.sourceforge.net/

enjoy

😛