There is a difference between being in an armed conflict and the enemy falling in battle, and having secured enemy as prisoners where they are at your mercy. I think that we can all agree (hold breath now) that summary execution of prisoners is a crime against humanity. The question then becomes what protections do they have? I have no problem with Nuremburg style trials (except I am opposed to the death penalty) for these prisoners. They get counsel, it is not conducted in secret, the proceedings are semi-public, they get a chance to defend themselves and if they are not guilty the verdict is public too.
The Nuremburg trials and the Adolph Eichman trial are fine examples of what civilization is about: trials are to show the public why the acts of the accused were wrong, and why the rule of law is right, even though inconvenient.
Now if the Chinese, Mexicans and Canadians had mounted a surprise attack on us all at once, the circumstances might be so dire as to require what Bush has proposed. But frankly, this conflict is so lopsided in our favor as to be unprecedented in history (and I mean no disrespect to the thousands killed in New York and Washington, but the only reason it was possible was because these were completely innocent civilians). There is no need to have secret proceedings. It is possible to have portions of the proceedings be non-public if intelligence sources are to be revealed.