I'll be damned … now I can answer my own query: Beta 1.3.0.1 works almost perfectly on Vista (x64) SP2 with Internet Explorer 8.
First-time installation of QTTabBar went as smoothly as I remember 1.2.2.1 on Vista 32-bit. Infinite gratitude to 'fresco', who has translated a compatible English xml file.
Tabs and tool bar w/buttons all seem to operate normally and the size of the search box remains stable. I am not using any of the 'new' plugins.
The only glitch I have run into — so far — is that adding an active tab to Groups produces a . Net Framework "Unhandled exception"; however, the 'Continue' button in this warning window allows the new group item to be registered and then ordered in Options. Once the originating Explorer View is closed, subsequent Explorer Views run without further error — until a new group item is added, and the cycle repeats. Since Groups are a long-term setting, this flaw barely counts as an inconvenience.
If Quizo manages a 1.5 or v2 update for Windows 7, I shall make a another donation with pleasure.
Quizo: wherever you are, thank you so much and good wishes!