Can I install Windows 7 on a MacBook Air without a SuperDrive?
The most straight forward method to actually getting this done is to get your hands on an external DVD drive that connects via USB but is not the point of your question.

Yes it is possible; you'll need to get your copy of Windows 7 DVD put onto a USB thumb drive. (There are several guides available online - I've not done it myself so I can't recommend one)

Another alternative requires a lot of extra work and is really designed if you're planning to image or install on multiple MacBook Airs; it's possible to NetBoot your MacBook Air using the USB Ethernet adapter. (Source) This requires either a rigged out version of Mac OS X or Mac OS X Server handy. With DeployStudio you can install a pre-made image of Windows 7 that way.