Majority of the newer MMO's offer widescreen support but even some of the newly released to US games will not have widescreen support being they're older games. You'll start finding problems when digging around with some of the older MMO's most of the time. As for forcing widescreen, it just depends on the game and if its possible. Some games have community made applications that force resolutions on the client or stretch the client to your designated X and Y. Alot of the 2d Side scrollers do not have wide screen support, other than that its basically a coin toss.
Honestly, EVERY MMO should support wide screen resolution. It's almost 2011, Widescreen monitors are used by so many people. There's no excuse for games not to support a decent wide-screen resolution imho.
