It looks like it comes with Win CE 5, so an upgrade to CE 6 is feasible
if Cowon offers one. Check with them.
Windows Mobile is basically just a variant of Windows CE.
Linux can run on practically anything * if * someone puts the effort
into porting/customizing it for this device.
Further questions about this device would probably best be
asked/answered in the Cowon forums here:
http://www.cowonamerica.com/forums/forumdisplay.php?f=90
technut