I found out about Quietnet from boingboing.net. Quietnet is simple python coding that allows you to communicate between computers via ultra-sonic sounds. All you need is python, speakers, and a microphone- something most laptops come equipped with. Get the Quietnet code zipfile from github here: https://github.com/Katee/quietnet
I had some issues getting it started, so I'm posting my experience to finally get it working.
As it turns out it appears that Quietnet was coded in python 2.7 so I re-downloaded that here using the 32-bit version that is compatible with the rest of the modules I found: http://www.python.org/getit/ This installation had to be done for - Just for me - and not for 'all users' which allows the python to be seen by the Windows registry...
Next I installed the necessary dependencies for Quietnet: pyaudio and numpy which are modules that are needed in python for it to work. I didn't get these files directly from the programmers, but got the binaries from an educational website that makes installation much easier: http://www.lfd.uci.edu/~gohlke/pythonlibs/
Make sure you download the 32-bit versions of the modules for python 2.7.
Once the modules are installed you can open up Python Idle to make sure they are running properly, do this by typing: help ('numpy') and: help ('pyaudio') You should see a bunch of info. without any errors and should see the version number at the bottom.
Almost done. Next open up the file send.py downloaded from github on computer using python. You'll get the > prompt. In another computer run the listen.py file. Make sure you volumes are up all the way.
So this should get you started, but its finicky using the 19100 Hertz for me. I had better results using 5000 Hertz. You can mess with the frequencies and other options in the option.py file.