Simon,
The problem is, once you boot your Mac into Windows, it becomes, for all
intensive purposes, a Windows box. All Boot Camp does is to allow Windows to
boot from the EFI, and it includes all the compatible hardware drivers for
Windows.
Having said that, your problem lies somewhere within Windows itself, and not
with your computer. You might check in the control panel and make sure your
screen resolution is set correctly, and also in your device manager to make
sure your video drivers are in fact installed correctly. Other than that,
try removing Hal, and then reinstalling from scratch. You know how well
Windows handles screen readers, and other such things sometimes.
*gives Microsoft the raspberry*
Jesse