If you have tried everything including reinstalling IE6.0, the next and final step would be to reinstall XP, starting afresh.. Reverend pretty much hit on all the bases, and it seems you have covered pretty much all I would have suggested even checking the registry prefixes.
So give XP a reinstall, backing up any important info like your favorites, Outlook contacts, my documents etc...

Sorry I couldn't offer any more assistance.
BB