Do U.N. resolutions ever expire?

[wuushew]

This was the legal basis for the United States invading Iraq. A more clarifying and precise coarse of action was to be defined by the U.N. but the U.S. skipped the "showing the cards" phase of diplomacy and headed straight to war.

Are U.N. resolutions the only tools that allow military action to be used against sovereign countries or does failure to consult inform the U.N. of one's plan of action constitute a breech of procedure if not international law?