Microsoft Corp., the worldÔÇÖs largest software maker, agreed to buy Greenfield Online Inc. for $486 million in a move that will strengthen its search and e-commerce services in Europe. ┬á The acquisition will boost Microsoft into the European market for shopping comparison Web sites that sell computers, cameras and other retail products. ┬á MicrosoftÔÇÖs failed bid for Yahoo! Inc. earlier this year left the software giant searching for ways to catch Google Inc. and boost its Internet business.