My high school French is just a bit rusty, but I believe that "Vista" is actually a French word; it translates roughly as "for people who've not yet bought a Mac". It makes sense, then, that the French would have something to say about Microsoft claiming "Vista" as its own:
French television presenter Philippe Gildas has sued Microsoft for "violation of intellectual property," accusing the software publisher of illegally using the trademark "Vista."
Gildas registered the name Microsoft chose for its latest operating system in October 2003 -- two years before Microsoft registered its trademark with the French National Institute for Intellectual Property (INPI).
He had registered the trademark for a new television channel aimed at senior citizens, Télé Vista, which was to have launched in 2003. The project was delayed, but is now coming to fruition, with plans to launch the channel later this year. Gildas sees Microsoft's hogging of the limelight with its new operating system as an obstacle to that launch, and so he decided to sue, arguing that he registered the trademark "in all entertainment and media categories: press, television, Web and so on."
That this challenge comes from France could cut both ways for Microsoft. On the une main, no one really cares if you steal from the French; on the autre main, once the French decide to fight you, everyone knows that they'll never surrender.
Personally, I think Microsoft should avoid the controversy altogether and simply market what's known (and much beloved!) as "Windows Vista" elsewhere in the world as "Windows Vichy" in France. That's just my €0.0148207, though.