In the meantime: Does George W. Bush have the legal right to plunge us into war with Iraq? It probably doesn't matter since if he tells the planes to go drop bombs, the planes will go drop bombs and — ta-dah! — we're at war, Constitution or no Constitution. I happen to feel his administration has unhesitatingly ignored that document in other areas and I don't see why this should be any different.
If however, you're interested in why he probably doesn't have the legal right, here's a link to a simple explanation by law professor Jeff Cooper. If you come across an equally straightforward counter-argument, let me know so I can post a link to it.