Have been trying to connect a web cam via an enhanced USB cable, but the audio is not very clear. Some discussion with JJ revealed that USB has different ways it transfers data.
isochronous is one way, and looks like my enhanced cable does not support this (I tried a non enhanced one and the audio was heaps better)
Check out http://en.wikipedia.org/wiki/USB  for more info on USB.
Our next solution is to try and use a
Webcam>USB-Ethernet Adaptor>Ethernetcable>USB-Ethernet Adaptor>PC
Apparently this will allow up to 100m extension which should be enough for my classroom web cam.
Next stop is to find a pair of inexpensive USB-Ethernet adaptors !