Wow! That's a tough thing to do. You see, to convince someone, anyone, the person has to have a desire to be convinced. He should be willing to let go of all prejudices and all the conclusions he's already drawn and be willing to listen to facts.
Fact is, Linux is free, to use, to modify and distribute.
Fact is, there are many Linux distributions.
Fact is, there is an extensive user community around each of these distributions.
Fact is, there are mailing lists, wikis, forums, irc channels, etc. dedicated to Linux distributions. So there's a lot of documentation and help.
Fact is, some Linux distributions are more user friendly, then others.
Fact is, you can do just about everything in Linux from the graphical interface.
Fact is, Linux distributions, are more secure then Windows.
Fact is, just about everything you do on Windows, you can do in Linux.
Fact is, there is excellent hardware support on Linux for wireless cards, webcams, etc. Most Linux distributions have their own Hardware Compatibility Lists, so you can also see what printer, scanner, etc. works on Linux.
Fact is, there is a difference between FREEWARE and open source or free software. What he's afraid of is FREEWARE. Linux isn't like your everyday freeware. It's Free Software. It's Open Source. It's reliable.
I could go on and on, but you get the idea.
http://opensource.org/
http://www.fsf.org/
Cheers!
[Modified by: Shashank Sharma on July 11, 2008 08:36 PM]
Coauthor of Beginning Fedora: From Novice to Professional published by Apress.
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