Can only boot to Windows 7, no OS
It sounds like the Windows reinstall overwrote your boot sector on your mass storage device.

I'd attempt to reinstall rEFIit, under Windows, and see if you can get the option to choose your boot partition on boot up again.  If that doesn't work, there's a new tool called 'rEFInd' that is actively being developed.  There's a good article here on using the tool with an HP laptop running Windows.

If that doesn't work, a clean start is likely in order.

You'll need an OS X install DVD and an external drive (or an appropriately bootable external drive with an OS X install image) to re-install OS X.

Once your OS is reinstalled, you can re-BootCamp the MB Air.