Simple Wireless networking with two computers
 

I have two computers runnng Linux. One is running Ubuntu 12.04, and the other is running Linux Trisquel. Neither are visible in the list of Wireless devices, although the Broadband hub is visible along with a number of other devices local to me in the area. I use an Ethernet cable for the main machine -Ubuntu - but it has a wireless adapter for networking to other computers. I have 'enable networking' ticked.

What type of ubuntu machine has a WLAN sending? (type, modell, HW informations)
Post the lspci result here.
I never heard of a standard PC where others can be connected via WLAN.
But, you could use "ethernet electricity" adapters. So, you would need no WLAN in your home. http://www.conrad.de/ce/de/overview/0415139/
I have such adapters for my desktops and connecting with wlan to a router for the laptops. VERY good things.

Typical Wireless mode is configured so computers i.e. clients can only connect to access points i.e. routers and therefore only they will show up on the wireless list. I assume the broadband hub is yours and you should be able to connect your computers via any networking protocol like ftp, ssh, SMB, ftp etc. It is possible to configure your computers in a peer to peer network where you can connect directly to each other.