Wifi not working in windows if thunderbolt display is connected
I have this exact same problem but in MacOS X Mountain Lion.  The minute I unplug the thunderbolt/minidisplayport, the wifi starts working again.

I found a weird solution on the internet from another Macbook Air owner witht eh same problem as us: access your router and change the channel to 1, or 2, or any other number that works.  For some reason, plugging in the cable disrupts the wifi signal entering the Macbook.

This seems to be a common problem and this seems to be the only solution that works, as many users have tried with different cables and different OS.  Hopefully Apple will provide a firmware update to fix this for good as not always can we access the router (like at my work).  However, as of today (I updated my OS to 10.8.4), this problem has not been fixed properly.

Good luck!!