zAlternator is an app that allows the Zune to sync with other software clients like Windows Media Player (WMP), MediaMonkey and even Winamp! From their site:
Finally, a release candidate of zAlternator is here! Yay! zAlternator is a program that will allow the Zune to be picked up and synced with programs other than the Zune program. It has been fully tested and proven to allow the Zune to be picked up and synced with the Zune program (duh), Windows Media Player 11, Winamp, and MediaMonkey. I have been unable to fully test the iTunes side of the program, but hopefully it should work.
While I love the Zune v2 software, the current lack of support for dynamic playlists and editing ID3 tag information is enough to turn me to WMP11. I’ll jump right back to the Zune software when the Zune team adds these 2 features.