OK so after reading through 15 pages of this I finaly have been able to get my Zune to sync.......I am running Vista Home Premium and was having the same issue as many of you. Installed updated software on the PC, but software was not recognizing the Zune via USB.
I first went to the device manager and under Portable Devices I selected Zune.
I updated the drivers by searching the web there in which it updated my driver. It seems to be that Vista had some issues and thinking my 80 GB was the old 30 GB. After doing this Zune Software loaded up on my PC as it had before.
I then went to device and my Zune started to sync by itself. As of right now it is syncing my 40 + GB of music.........Hopefully this works for you.
Yes we can and yes we DID!