IF06 - Rockbox may be a better solution for you as zmatt said I looked around and it looks like zen's are supported, It would be a lot easier than moding the Ipod Linux source code to do what you want it to do.
Yeah, well I assumed from the iPod linux forum that it's mainly just iPod since the offtopic room is the only room I can post about linux to zen topics.
you would have to recompile the source so that it could be run on whatever form of processor is embedded in the Zen.....a generic kernel sure as heck wouldn't cover it because i have a feeling it's not X86 based.