Messenger Services
Are you looking for a way to communicate with your friends online?  Even if you use Yahoo! Messenger and your friends use Google Talk, you can all still talk to each other.  Click here to get an overview of at least fourteen free web-based instant messenger programs.  Web-based means you don't need to download any software to use them and since the library doesn't allow downloads to the computer lab PCs, this is a great solution!  Scroll down to the bottom of the linked page to see a comparison chart.