Thanks everyone!
Sorry, couldn't reply to this thread earlier as I was ill. I took all suggestions into account ( well atleast those which came in before my scheduled lecture ). The lecture was very well received. The Freedom aspect, 3D games on Linux, Music, Chat Messenger, and other facts really got their attention. And the most important thing that REALLY got them to sit up and take notice was the fact about viruses, spyware etc... When I asked if anybody bought a legit copy of windows - all said no! When I told them that what they were doing was illegal and they could be thrown in jail for it, they really got scared =P hehe. Anyway, when I told them the virtues of Linux and the fact that I get sound sleep because 1. I am not pirating software. 2. I am assured that my system is safe :) They were very impressed :)
Once again, thank you for the suggestions!