This is the oficial website of virtualenv, where you can find infromation about the installation and the usage.
If you are connected to the Internet from Erle(by using a wireless nado usb) then you only need to type:
root@erlerobot:~# pip install virtualenv
If not the process must be a bit more tedious:
First of all yu need to download the virtualenv
from here
Download the file called virtualenv-1.11.6.tar.gz (md5, pgp)to your Pc. Then copy it to Erleboar, you can find in this tutorial how to do it.
Once you have copied it, type :
root@erlerobot:~# tar xvfz virtualenv-1.11.6.tar.gz
root@erlerobot:~# cd virtualenv-1.11.6
root@erlerobot:~# python setup.py install
Congratulations you are now ready to use it!