That's because the iPod's storage is formatted as Mac OS X Extended Journaled. You need to reformat it as FAT32 so that the iPod's flash storage is Windows formatted. The FAT32 file system type can be read and written to by both OS X and Windows.
A Mac formatted iPod can be read or written to by a Windows PC.
To set up the iPod as a Windows formatted iPod, simply restore it in iTunes on your work PC.