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I have a mid 2011 MacBook Air (Mountain Lion) which is currently running Win XP under Parallels Desktop.

Is it possible to install this under Bootcamp instead?

Probably not. Mountain Lion's version of "Boot Camp" (Apple's combination of drivers and partitioning tools to install Windows) only supports Windows 7.

You probably couldn't even technically install something as new as Vista - I believe I tried when I had a 2011 MacBook Air. It installed but had no video acceleration. or wireless, etc.
 
This might be a lame question. If so, I apologize.

Using Bootcamp, is it possible to run different versions of Windows? If I install XP as instructed above, is it then possible to also install for example Win 7 - giving me the choice of running OS X / XP / WIN7?

Cheers
 
With BootCamp, I don't believe it is possible to run two or more flavours of Windows OS.

With VirtualBox you can run more than one version of the Windows OS.

Also, Microsoft offer 'VirtualPC' alongside Windows 7 Pro & Ultimate (once a strictly Mac virtualisation program), that enables you to run 'XP Mode' within Windows 7. This may be a solution for you.

http://www.microsoft.com/windows/virtual-pc
 
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