How did you get them on the Zen in the first place?
Load ......... Creative Media Source .... plug in your zen .... in the right hand pane click the "small drop down arrow" and select your Zen player. This should show all the songs you have on it. You can select them and using the arrows to the left of that list click the one that points to the left and your songs should be moved to your PC Library.
This is easier than it sounds .... something similar with Windows media player but beware of syncing and syncing in the wrong direction - i.e. wiping your Zen.
I have Creative Zen, Touch and a little one (can't remember the name)
Good luck.