I just tried and was a bit surprised it did not work.
I did figure it out though.
On the status bar of the VM, on the lower right hand side, you should see several icons, the first 3 are USB symbols. Click once on each one until you figure out which one is the iSight and click "Connect iSight", it will then go through the standard Windows installing new hardware bit.
Of course you will not find the drivers
They are apparently on the Leopard disk, but after a little surfing I found old ones at
http://makel.org/articles/53/
The ones from makel are for a macbook pro, the MBA is a little different. If you want to use them you need to edit the iSight.inf file so that the lines under [Apple] are like below:
%isight.DeviceDesc%=iSight,USB\VID_05AC&PID_8505&MI02
Then update the driver from Device Manager, you will get an error, but if you open the Camera and Scanner Wizard you will see it works. I do not have any IM SW installed, so I cannot test it any other way.
Good luck, you are probably just better off using the CD.
Good luck.