Well, neither I do except for installing msn only for you nad not for all the users or blocking it with firewall. Anyway, how many messages and chat are they receiving btw? And how much do they study? I usually study about 2-4 hours depending on the lessons I have the next day (without the projects we have for weekends). It's not much I would say, cause I am a really good student (94% overall) and besides the studies are quite difficult specifically on Ancient Greek and Algebra and I need some tme to achieve a high mark.
I modified my friends pc so that he will be able to view the actions of his sister on the windows and internet and block her to run some programms through Vista parental control. I also modified the schedule that she will be able to access the pc, so a chance to do that is by installing vista, if you are planning to you could do it now. Another thing you could to is to buy a pc of your own so that you could access it privately and then modify their pc not to allow msn to run. The most perfetic but efficient way to prevent it is to take off the phone cable from the pc on study hours, but I'm sure you'll end up with having about 2-10 phone cables depending on how much of their budget they would give to buy some.
Block MSN 
Linear Mode
