"The question I have for you is: Why did we choose to invade March 2003? Why not before he invaded Kuwait or Iran or when he was fighting the Russians for us? "

When was Saddam fighting the Russians?

I'm afraid you been a sucker to the story that Saddam was our buddy.
Moore and pack of other lefties have been trying to rewrite this. Most people who have a few brain cells functioning dismiss these attempts at rewriting the facts as merely "rhetoric" [strawmans and building on the tinest speck of "possible truth"]. Of course it's just gravy when the "useful idiots" actually fall for their suggestions.

For example, Bowser has "apparently" completely bought the idea that Bush is a liar. Now, it might be that "bought" is too strong a word. It implies some reasoning and reaching a conclusion, whereas Bowser may be acting like a dog that upon hearing sirens, barks in response.

Saying that Saddam was fighting the Russians for us is almost as false as saying Castro was fighting the Russians for us. At best Iraq was a non-aligned country [Cuba also claimed to be non-aligned whereas India actually was the closest to being a true non-aligned state- on the other side of the coin Saudi Arabia claimed they were non-aligned {though they were definitely a US ally}]. Of course, with the end of Cold war, "non-aligned" lacks definition- though some, of course, would like to twist it's meaning to become "against any and all US interests".

Oh well, here is some historical reading on Non-aligned countries:
http://demo.sakhr.com/diwan/emain/Story_Of_Kuwait/Independence/Kuwait__World/non_alliance.html