For quick reference,
THIS is the article Obama wrote for the paper, mentioned in the wiki.
I would also like to point out an interesting element to the whole story - The Pakistani friend who taught him to cook curry while he was at Columbia (see wiki). Look at the changes they say took place while he was there -
Went from being a drug user to being clean. Began pursuing physical fitness. Withdrew from the world around him.
Maybe trying to connect to his Fathers roots? No smoking gun, but if I had a friend of the same background as him, at the same stage in life (at University), I would be watching very closely for any signs of radicalism seeping into his discussions on politics, religion, culture, etc, given the other changes that were obvious. Not drawing any conclusions here... I'm just sayin'.
-out