OK, firstly I don't even know whether something like this exists but what I'm looking for is a USB extension that goes from the output of speakers designed for iPods, like the male connector of the USB connection to the input of the mp3 player. I have a Zen Vision, 60GB and doubt this will fit in the slot for the iPod so it will not be able to plug in.
The speakers I have purchased are http://www.amazon.co.uk/Istation-Speakers-Docking-Charging-warranty/dp/B000RVHWLW/
Logic 3 Istation Speakers . It has a what looks like a USB 2.0 connector on the back but I'm not sure how that would help connect something to it, rather it would connect THEM to a computer.