Presidents have declared war on Germany, Japan; Korea; and Vietnam without Congress's prior approval. They just go with the flow. Include Desert Storm too. Congress surrendered wartime decisions to the Executive Branch. I honestly don't know the logistics; I just know what I've seen on the internet and different books.
Or, check out this from MSN Encarta on who can declare war:
"The president of the United States has no clear constitutional authority to declare war without congressional approval. However, the U.S. Supreme Court has determined that the president, as commander-in-chief of the military, does have the authority to recognize a "state of war" initiated against the United States and may in these circumstances unilaterally send U.S. troops into battle. President Bush has also stated that his powers as commander-in-chief allow him to act independently in defense of the nation.
The president did not seek a formal declaration of war from Congress. But he did seek congressional support, he said, to demonstrate to the United Nations and to the world that military action against Iraq was not just his own objective; it was a view supported by the American electorate as a whole. Strategically, support from the legislators bolstered the president's case as he pressed the UN Security Council for a resolution authorizing military force in Iraq."
......Um..... can somebody say dictatorial powers?