Step 3: No USB boot? Install rEFIt!
Not all Macs support booting from a Windows-formatted USB thumb drive. So if you don't see an image like the one to the right after plugging in your Windows USB key you're going to need to equip your Mac with rEFIt, which enhances the standard EFI with a few options such as a terminal command line or our much-needed USB boot option. And it's not as complicated as it sounds: Just head over to http://refit.sourceforge.net/ and get the 6.5 MB DMG file. Install rEFIt and restart your machine. Note: It might take a restart or two until the rEFIT option shows up, so be patient.
Step 4: The Windows 7/8 Setup
Once you've booted from USB or DVD, you've basically survived the most "difficult" part. I won't bore you with the details of how to install Windows on your machine -- it's the same old procedure as ever. Both Windows 7 and Windows 8's setup steps are fairly simple -- just make sure to select the "Boot Camp" drive during setup and let it run its course.
Note for Windows 8 early adopters
The Intel HD 3000 Graphics on the 2011 MacBook Airs and Mac Minis have some problems with the built-in Windows 8 drivers; which makes the lower half of the display flicker and indistinguishable right from the setup. As you might imagine, that makes it kind of hard to work with or even finish the setup! The easiest solution is to plug in an external display, which shouldn't be affected by the glitch. If that's not an option, you need to use your mouse and/or touchpad to guess where to click next on the Windows 8 installer.
Once you've gotten past that small hurdle, download the latest Intel HD 3000 Graphics drivers for Windows 7 and unzip the file, because you're going to need to do a bit of driver tinkering in order to get your graphics to work: Open up the subfolder "Graphics" and look out for the "igdlh.inf" (32-Bit) or "igdlh64.inf" (64-Bit) file. Open it and replace the line "no install on Win8" with the entire paragraph you see under the line "[IntelGfx.NTamd64.6.0]". Click on the following screenshot to see how it works: