Finding Friends   Foes (Forbes.com) Forbes.com - Tens of millions of people play videogames online; the tricky part is finding your friends--and favorite foes--among them. Michael Cassidy can help. His company, Xfire, runs a Web site that is the TV Guide, ma icirc;tre d' and instant messenger of the gaming world. Cassidy's service can point you to a buddy who is ready to play the game you want at any moment of the day or night. He already has a lot of friends to prove it. In eight months a million people in 100 countries have downloaded Xfire's software.