Targeting Homeland Security Resources Effectively Against Terrorism Act of 2006 (THREAT Act) - Directs the Secretary of Homeland Security to carry out a program of discretionary grants for use in high-threat, high-density urban areas. Directs the Secretary to make grants to not more than 15 areas in a fiscal year after considering the population, presence of critical infrastructure, and credibility of the terrorism-related threat for an area. Requires amounts awarded to be disbursed directly to local governments.