How to make Bootcamp 4 work in Windows 8.1 on unsupported MacBook Air 1,1
I fixed this issue by right-clicking the setup.exe file in Bootcamp and choosing "Properties". I set the compatability setting to "Windows Vista Service Pack 2" and ran it as administrator. I got a compatability warning but chose to run program anyway. The Bootcamp program ran, installed all the drivers and (importantly) the Boot Camp option on Control Panel. Meaning that the keyboard is now the correct UK Apple version and the trackpad has tap to click and I can right click by tapping both fingers. This old MacBook Air is actually pretty usable on Windows 8.1 and its supported until 2023!