I'm going to say that -- speaking as someone who knows absolutely nothing about using a Zune -- probably not.

The one thing that might come up, though, is that iTunes will probably want to copy all of the music files over into it's own set of folders (which is probably all for the best, anyway, if you want to avoid conflicts with the Zune's software), so I'd take care to have a backup copy of those music files before installing iTunes, just in case they're moved (instead of copied), and the Zune program can no longer find them.

Hope this helps!

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