http://www.allcam.biz/catalog/product_info.php?cPath=29&products_id=247
and buy the long arm modules, im running a dual setup (60 quid) and its faultless
maybe its cheaper to buy 2 duals as you dont need any extra arms and then you have the possibility of 4 if you want it?
Erm - check the drawing in link - it clamps to the back of the desk, like a G-clamp.