W7 /Vista
video drivers fail for many users (no upgrade avail).
It is just simpler to say NO W7 / Vista compatibility than to try and enumerate which work (Just think of the effort to log

)
You are free to try

, just don't cry if it does fail

(This fail does not damage the Library, so just uninstall, and install the old version.

I keep the last 2 regular releases handy, just in case)
OTOH Calibre 2 slammed into XP limitations for the majority, so The installer just rejects XP installations