basic open source 101

[Ervin Gong]

I am a student from the University of Hawaii and I have a few 
questions that i hope you all can answer regardinig this topic.  i 
hope that you could shine some light into this subject for me because 
of my lack of computer knowlegable circle of friends.  my questions 
are:

open source goes against many of the things taught in business (my 
major), where most people are very protective of their intelectual 
properties.  
-why do people want to share their knowledge for no profit?  
-what does companies like IBM gain from putting their source codes for 
everyone to see?   
-would IBM be able to use the source codes contributed by open source 
and sell it for a profit?  
-can anyone make addtions to the source code and not reveal it to the 
public?  
-redhat sells a enterprise linus and other software for $349.00 that 
doesn't sound free to me?  any reason why they can do that?

please excuse my ignorance if any of these questions are "dumb" 
questions.  hope to hear from some of you.

ervin