Then one can use the file compare utility to see what changes have been made:
Note when exporting the registry hives in Windows 2000,XP,2003 then they are exported as unicode (Windows Registry Editor Version 5.00). To perform a file compare on two unicode files:
FC before.reg after.reg > diff.txt
Note instead of exporting the registry, then one could also use Process Monitor by SysInternals.com to see the registry changes made by an application.
FC before.reg after.reg /U > diff.txt