For some inexplicable reason Zune playlists (ZPL) are different from Windows Media Player playlists (WPL). I foolishly made a Zune playlist and wanted to burn a data CD with it, but the Zune Burn feature only makes audio CDs. I tried loading the ZPL into WMP, but it failed. After 60 seconds of comparing two files, here is what worked for me. YMMV:
Open the ZPL in your favorite editor (e.g. Notepad). In the first line change
Save As the file with a wpl extension.
I could then load the new WPL file into WMP and easily burn a data CD, for use in my car.
WPL files at least are somewhat described on MSDN, I can't find any definitions for ZPL files though they appear to be identical save for the header and the file extension. ASX files are yet another Microsoft playlist format which I have had some experience of.
Note that this shold not be considered Official Microsoft Documentation. But its the best I can do, hope someone finds it useful.