From the TweakVista Public Beta Released! article (down at the bottom):

Thank you for responding GreenReaper. There is a grayed out OK button at the bottom. We can only see the top half. We were on that screen for almost 2 min. maybe? and it never changed. GreenReaper, you said "it is grayed out to start with but should become enabled shortly afterwards." Maybe we need to wait longer?? I would think it would have done something by then. I don't know. I spent 34 min. on the phone with tech at StarDock. He sent me another copy of TweakVista, brought it over to my neighbor & the same thing happened. I was on the phone with him the whole time. He was a little baffled at that also. (Note: I have no knowledge of Vista so I was a little lost ☺) Anyway, I got disgusted at my neighbor for not knowing her way around Vista so I told the kind tech support that also & I said thanks for his help & our goodbyes.
If you can help any further with any other suggestions I will keep checking this thread.
Thank You again