I downloaded a 20-day trial version of Compare Spreadsheet for Excel,
installed it, and tried to run it. It gave me an error and crashed. I
uninstalled it, and tried to install it again. This time
*installation* crashed.

Not an auspicious start. Which is too bad, because I seriously need a
rapid way to compare similar (but with small crucial differences)
Excel files.

I have Windows XP machine.