You don't want to use a USB cable, you want to use CAT5 or 5e Ethernet from the wireless router that you will convert into a client bridge as in
THIS picture.
But before buying anything, it is best to find out what model wireless router they are using (and if they know what frequency and is set for N only or also legacy G devices). Find that out and post it. Also, I would suggest downloading a free wireless analyzer called inSSIDer from
HERE and run it in some different locations to see what the best signal strength you find for their wireless (it will be in -dBm and lower as in closer to zero is better, a stronger signal).