The International Court of Justice can demand new trials for foreign citizens in the US who weren't told they could contact their embassy or consulate. President Bush can order that States will comply with the ICJ.
However, the States don't have to pay any attention to either of them. The part of the Vienna Convention which the ICJ and President tried to enforce is not self enforcing. In other words, when the treaty was approved by the Senate and signed by the President it did not state that it would become law within the signatory countries. Therefore, in order for the treaty to have force of law within the U.S. the Congress had to pass a law enforcing it.
Congress did not. Thus, the President as chief of the executive branch had neither power to enforce under the treaty itself nor power to enforce under a congressionally mandated statute. He had no power to execute and his mandate that the States enforce is unconstitutional.