VNC over USB tether?

Edit: I want to connect to a vnc server on a PC from an Android client via usb tethering. I'm trying to use my phone as a way of interacting with a headless linux box. I can't get VNC or connectbot to work with usb tethering - they just time out. Work as expected when I connect the phone through wifi. Is there something I need to do to make this work? Open some ports or something? I could get primitive ftp working through a USB tether. Anyway I'm in need of suggestions of where to start looking - or if it is at all possible. Wifi and bluetooth don't suit my use-case Cheers