Computer Lab

This year, one of my goals has been to set up a computer lab.  I wanted to use a separate computer and keep my recently purchased one strictly for the business and my use so I put a bit money into a used one rather than buying another new one (which I couldn't afford right now!).  I've done a bit of research into it and have to admit that I am not very "hardware" saavy, so I'm starting with a basic set up - a separate computer with some on-line games as well as some software that I will purchase.  I have a midi and Finale, and plan to use that set-up for a couple of my more advanced students. 

Right now I'm in the midst of putting together a letter to my parents, figuring out how much extra to charge and organizing a lesson plan for each student.  I would LOVE suggestions from any of you who may already have this set up.  My plan is to have one student taking a lesson while another is working at the computer.  I'm trying to figure out how much is fair to charge and what programs would be the most effective to start with.  Any help that any of you can offer would be greatly appreciated.