When installing a 64 bit version of Windows on a MacBook Air, I had the error message "Boot Camp x64 is unsupported on this computer model", apparently because Apple does not support 64 bit Windows on MBAs. I found a simple solution at http://michael.anastasiou.me/index.php?option=com_content&view=article&id=22:qboot-camp-x64-is-unsupported-on-this-computer-modelq-solution&catid=7:how-to&lang=en.
Speaking of Boot Camp, it's irritating that the Windows drivers are ONLY available on your Mac OS install discs. If you're installing Boot Camp, you need your OS X discs to install it properly. This is troublesome if you've lost the discs or don't have them with you.