That's interesting - Final Fantasy XI worked fine and the first thing it does is install new crap all over the place when you start it up =] Except for the occassional crash due to bad graphics engine.
Just re-enable the 'proper' administrator accound that is disabled by default.
That never actually solved it for me.
I also read of adding 'TrustedInstaller' rights to the admin account and using that, but I guess that must have been fixed post-beta2 cuz it didn't seem to make a difference for me.