In the thread, the guy with As said he had about a 75% chance to win and backed it up with numbers from http://www.twodimes.net/poker/. But the guy with 3s had only four outs (the sixes, since the other two threes would give As a straight) or he would lose. According to the statistics as above, that means he only had a 16.47% chance to catch a winning card, making the guy with As about a 83% favorite. I say about because I get that if both a 3 and a 6 came then they would tie with a straight to 6.
Just to clearify - he does have 6 outs, because the 2 As also give him a straight. So he now does have 6 outs.
6 outs is about 23%, plus he could hit runner runner3, or 3-5 or 3-4, giving him 4 of a kind or a full house.
As for the rest of your question, I am not a math wiz, so I go to the ultra basics. You have almost a 2% chance to hit any card in the deck. So give yourself 2% per out, per card remaining.
6 outs - with 2 cards remaing is about 24%.
That's pretty close to the 75/25 the guy with AA said he was.