why not just stop free radicals?

[jmsdean at pipeline.com]

can someone please explain how free radicals are formed.  there's lots of
talk about the body forming free radicals when the cells use oxygen but i'm
not sure how this is done.  
 
secondly, what is the chemical structure of a free radical. 
 
lastly, why is stopping free radical production, as opposed to using
scaverngers like anti-oxidants, not a current possibility.   
 
luke