I realise it's now a good few months on, but I wanted to just record my thanks to Anonymous for posting the above, which seems (so far) to have solved this issue for me on Vista. Much appreciated :-)
In case it helps anyone, the path for achieving the same thing in Vista is as follows:
Right click 'Computer' then go to 'Properties'>'Advanced System Settings'
Then choose 'Settings' in the 'Performance' box and uncheck "Fade out menu items after clicking"