We used to use the USB method and worked quite well, but on the last upgrade I was determined to get all PCs to boot from lan. I was already using ghost and never got my head around how you integrated all the drivers for different PCs onto a RIS image so I stuck with ghost. So now use boot to RIS, RIS then loads a ghost image. Takes about 15 minutes to rebuild 30 machines to the OS stage. I spent a lot of time getting a ghost image to cover all my PCs so didn't find the need to pursue the RIS image, I may change my mind later when having to repurchase ghost licences.
P.S. The driver packs website looks good contink, glad I read this thread.