Try opening device manager (Windows+Pause/Break, Device Manager in Windows 7, Windows+Pause/Break, Hardware, Device Manager in XP). See if any funky 'no driver' yellow question mark devices exist in the list. Also worth seeing if the Empeg appears in there anywhere. Try updating the driver and forcing the driver to be the one in the Emplode zip that you downloaded.

Or, of course you could just give up on USB. Plug the Empeg into your switch/router and see if Emplode finds it over the network.

If you're still having problems, take a look at the Riocar bible.