Yahoo answers is a forum like all the others, but the goal is different... people ask questions, and the members give answers... no discussions.
if you want to have the same kind of look, you simply have to edit the templates to make it so... and apply some rules on your forums to make it follow the same kind of participation from members.
the only other solution you'd have is ico-content, that is grabbing yahoo answers content and put it in your forum, the way you wish...
http://www.icomotion.com/ico-content/index.html (built by a guy from here btw!)