Rumsfeld can not resign, the anti-war crowd would have a field day at conformation for a new SoD, but Runsfeld needs to realize he's no where near as smart as he thinks he is.
Take a gander at Rumsfeld's resume. Do you think that his impressive record in public service and private business reflects someone who doesn't know how to manage people and resources? The disgruntled generals are unhappy that we have a SecDef who actually runs the Department of Defense and doesn't act as a figurehead. They also have a personal agenda. It has more to do with the generals' egos than Rumsfeld's. He doesn't have anything to prove.