Is it impossible to install windows 7 via boot camp in a lion based macbook air? I have installed windows xp/vista through bootcamp with snow leopard (boot camp 3.x) several times. After a fresh installation of lion on my macbook air, something has changed.

With boot camp 4.0, I cannot create a bootcamp partition for windows 7 without external cd-rom, which would not occur with snow leopard. I tried to use usb stick and virtual windows 7 cd on the usb stick however, both not work.
It's possible.  


Create a partition for Windows.  
Get the Windows 7 USB DVD download tool.  Create a bootable USB installer.  
Boot from the USB stick and install Windows to the partition you made.


If you already tried the above, what error do you get?