That's just a way to avoid having to boot into Safe Mode with networking.Instead of booting into safe mode with networking,people could make sure "download updates immediately" isn't checkmarked on the select components screen when installing Spybot in safe mode,then download updates after they're out of safe mode.
Did you get any errors when you tried to run the installer in safe mode again,or it just won't run?
You could click Start,type Problem Reports and Solutions in Vista's search box.Doubleclick Problem Reports and Solutions,and then click 'Check for new solutions' in the left-hand column.Does it list anything there?