I have the same problem with 2007 Professional with XP Pro. I can't use
Word, it just keeps restarting the setup process on entry and proceeds
without error, requesting I reboot after successful setup. Then I reboot,
restart word, and the setup process starts anew. Installation is successful
according to the event viewer. I see nothing peculiar in the event viewer.
If I don't reboot after successful setup, I get the setup starting again in a
few seconds.