The download is a set of inf's for differrent non-Vista OS's; XP, 2k, ME (at least I don't remember a Vista version.
Once downloaded, plug in you USB ethernet adapter, and when the hardware wizard asks for a driver ... specify the location of the inf you need for your OS
I wonder, whether there are different versions of BootCamp drivers floating around. I used my Install Disk for the Air to install BootCamp (not an older Leopard Install disk.)
I later plugged in the Apple USB Ethernet adapter, and it configured and worked without trouble.