Substral

Hmm.. if it's a non-Domain computer, you should be able to restrict it quite nicely with Parental Control and Local Group Policy.. Parentals can limit the websites you can visit (iirc) and there's "allow use of these programs" -type setting to allow only web browser and media center, which should deny running any other program. And to make sure, you can use Security settings to deny Task Managers and other tools that could be used to easily open other progs.

Happy configurings, I hope you get some progress with this ^^