Yao would win a fight easy. Pacquiao would all be trying to fight with fists and stuff. All Yao would have to do is choke slam him. Getting choke slammed by a 7'6" guy? You don't get up from that.
I'd take Paq, Yao would probably try to take a charge then wind up with Paq on his chest hacking away Wolverine style.
I bet Yao would rather get hit square in the forehead, rather than the place Paq could easily reach with his short stature
I love Yao but he would definitely loose! Pacquiao is a professional boxer who has reached the pinnacle of his profession. He knows how's how to throw punches and dodge punches and knows exactly where to hit a person to disable their mobility! He feels comfortable fighting because this is what he does, he also has the killer instinct that you really can't teach a person, either you have it or you don't! Yao as much as I love him is slow and probably has never thrown a punch in his life. The only thing he could do is try to grab Pacquiao and to that he would have to bend down and leave himself exposed! His height is actually his downfall! He has to come down to Pacquiao and in doing so puts himself in Pacquiao's wheelhouse. This would be an awkward fight but one that Pacquiao should win! ....... ....... .......
Protip for short guys fighting NBA centers: Please refer to Bruce Lee vs Kareem Abdul Jabbar http://www.youtube.com/watch?v=Mjks2kiCPXo
Are we talking street brawl or boxing match? Why wouldn't Yao just kick the $h!t out of him with one of his gargantuan legs?