I've been using it with Vista since the RC Vistas in 2005/6. No problems.
The latest versions of BspEditor do not use the registry, which is a good thing. But in the very latest (last) version, the facility to link with Tony B's utilites was removed so I have stuck with 96b.
I have written my own Utilites GUI in VB and would recommend others (if you have programming knowledge) to do the same. This means I can call up the GUI from within Bsp Editor and amend all of the parameters for the three main utilities (Qbsp, Light, Vis) and effectively stay in BspEditor.
I've used it for 10years and as you probably have guessed, I rate it.