National Commission on the Modernization of the United Nations Act of 2003 - Establishes the National Commission on the Modernization of the United Nations to study: (1) the extent of modernization of the organizational structure and practices of the United Nations (UN) that can be effectuated with and without changes to its Charter; (2) the principles to which member states should adhere and the consequences of a state espousing and enforcing values counter to the Charter; (3) the feasibility of mandating each member state to agree to adhere to the principles of UN membership, and to review the principles of the UN to determine whether the state should withdraw if the UN is not adhering to the Charter; (4) whether all states should have one vote in the General Assembly and whether the UN should be structured in a bicameral fashion; (5) whether auxiliary commissions and organizations of the UN should be funded by member dues, whether such entities drain resources away from the primary function of the UN, or whether member states can create and fund caucuses to deal with matters of common interest; (6) whether the UN should have a separate peacekeeping force, while identifying successes of past peacekeeping and humanitarian efforts; and (7) the credibility of resolutions when the UN does not mandate absolute obedience.