Since the google groups interface won't let me reply in a thread, even
though I'm subscribed, let me say that Christian's solution works.

The problem: Vista suddenly stops recognizing the cd/dvd drive. New
software media does not come up ready to install, instead, nothing
happens. When you click on the the drive in Explorer, you get a
message asking you to format the disc.

The workaround: Click on format, after some messages, it tells you
that the disc can't be formatted because it already has stuff on it.
Now when you click on the drive in Explorer, the files come up and you
can go ahead and install your new software. Unlike Christian,
however, I have to do this every time.

I wouldn't do this with a rw type cd/dvd, only with manufactured ones
where you can be confident that the media is not formatable.