There's a wireless router in the building. I've had a look round each of the rooms and cannot spot it. Is there any way I can track down where its physical location is? I suspect it's hidden down the back of a desk/cupboard or something insanely stupid.

Do you know the locations of the sockets? If you can you may be able to work out which one it's connected to and then follow the cable.

Wireless sniffing will be tricky tbh.

Use a wireless sniffer on a mobile or laptop then walk around until you find the strongest signal

Yep

Use InSSIDer - it's free and gives you a signal strength reading.

Triangulation would probably do the job. There are other wifi sniffers that will draw a 'heat map' of an area if you walk around it enough, that might be your best option. Hottest spot = where the router is.

I was hoping an iphone gadget would be useful but I don't mind bringing in my netbook.

Thanks for the help