I am not really the one to answer this but it has sat here nearly twelve hours, which seems rude, so I will give it a go. IMO the key would be how you use it. If you set up a website about something completely different you might be OK, if you clearly were playing off the Zune name they would have a case against you.
And do not even consider hawking it to the Zune folks, unless you have owned it much longer than the Zune name has been known.