There has been some speculation about the word Zune around the Internet. I myself have wondered how they came up with the name, and I think I've figured it out.
Microsoft has a few favorites that they seem to keep coming back to. One of their favorites is "Active", as in Active Directory, Active Content, Active Server Pages, Active Desktop and ActiveX. That last one is where the "Actives" intersect with their other favorite X. As in XBox, ActiveX and DirectX. Since they wanted to tie the Zune to the Xbox via the Marketplace I think the original name for the device was planned to be Xune, springing off of their "X" brand and because it's a direct competitor to iTunes and since calling it Xtune (or xTune) would have been too blatant a ripoff.
The problem being that nobody can seem to agree on how to pronounce words that start with the letter X. Is it egzune (like Xavier), zune (like xylophone) or tenune (like Mac OS eks, but if it was called ten-une it would only be a matter of time before people started calling it eleven)? Market confusion is something that Microsoft definitely does not need while trying to take on the ubiquitous iPod and its rock solid brand. They already have enough problems as it is. That's when someone from Microsoft's marketing/PR/whatever decided to solidify things by changing the X to a Z.
Then somebody goes and z-unes it up by pointing out there's already a Hebrew word by this name.