Department of Homeland Security Appropriations Act, 2004 - Title I: Departmental Management and Operations - Makes FY 2004 appropriations to the Department of Homeland Security (Department) for: (1) the Office of the Secretary and Executive Management; (2) the Office of the Under Secretary for Management; (3) Department-Wide Technology Investments; and (4) the Office of the Inspector General. Title II: Security, Enforcement, and Investigations - Makes FY 2004 appropriations for: (1) the Office of the Under Secretary for Border and Transportation Security (salaries and expenses, and U.S. visitor and immigrant status indicator technology), (2) customs and border protection (salaries and expenses, automation modernization, and construction); (3) immigration and customs enforcement (salaries and expenses, Air and Marine interdiction, operations, maintenance and procurement); (4) Federal air marshals; (5) the Federal Protective Service; (6) the Transportation Security Administration (aviation security, maritime and land security, intelligence, research and development, and administration); (7) the U.S. Coast Guard (including a rescission of funds, operating expenses, environmental compliance and restoration, reserve training, acquisition, construction, and improvements, alteration of bridges, research, development, test, and evaluation, and retired pay); (8) the U.S. Secret Service (salaries and expenses); and (9) acquisition, construction, improvements, and related expenses. Title III: Preparedness and Recovery - Makes FY 2004 appropriations for: (1) the Office for Domestic Preparedness; (2) firefighter assistance grants; (3) the Counterterrorism Fund; (4) the Office of the Under Secretary for Emergency Preparedness and Response (including for securing medical countermeasures against biological terror attacks); (5) the Radiological Emergency Preparedness Program; (6) disaster relief; (7) the Disaster Assistance Direct Loan Program Account; (8) the National Pre-Disaster Mitigation Fund; (9) the Flood Map Modernization Fund; (10) the National Flood Insurance Fund; (11) the National Flood Mitigation Fund; (12) emergency management performance grants; (13) emergency food and shelter; and (14) Cerro Grande fire claims. Title IV: Research and Development, Training, Assessments, and Services - Makes FY 2004 appropriations for: (1). citizenship and immigration services; (2) the Federal Law Enforcement Training Center (salaries and expenses, acquisition, construction, improvements, and related expenses); (3) information analysis and infrastructure protection; and (4) science and technology (research, development, acquisition, and operations). Title V: General Provisions - (Sec. 503) Prohibits the availability of funds provided in this Act, provided by previous appropriations Acts to the agencies in or transferred to the Department, or from any accounts in the Treasury derived by the collection of fees available to the agencies funded by this Act for obligation or expenditure through a reprogamming of funds that: (1) creates new programs; (2) eliminates programs, projects, or activities; (3) increases funds for programs, projects, or activities that have been denied or restricted by Congress; or (4) proposes to use funds that have been directed for a specific activity by the appropriations committees for a different activity unless such committees are notified 15 days in advance. (Sec. 505) Authorizes the use of appropriated funds for FY 2004 and thereafter for: (1) the purchase of uniforms without regard to the general purchase price limitations for the current fiscal year; (2) the purchase of insurance for official motor vehicles operated in foreign countries; (3) entering into contracts with the Department of State to furnish health and medical services to employees and their dependents serving in foreign countries; (4) the employment of experts and consultants; and (5) the hire and purchase of motor vehicles. (Sec. 508) Deems any funds made available by this Act for intelligence activities to be specifically authorized by Congress under the National Security Act of 1947 during FY 2004 until enactment of an Act authorizing such activities for FY 2004. (Sec. 509) Directs the Federal Law Enforcement Training Center to establish an accrediting body of both Federal and non-Federal law enforcement training experts to establish standards for measuring and assessing the quality and effectiveness of Federal law enforcement training programs, facilities, and instructors. Requires the Center to ensure that all training centers under its control are operated at optimal capacity throughout the fiscal year. (Sec. 513) Prohibits the use of Department funds: (1) for the production of customs declarations that do not inquire whether the passenger had been in the proximity of livestock; (2) for any activity or Government employee salary that would prohibit the enforcement of the ban of the Tariff Act of 1930 against the importation of goods mined, produced, or manufactured by convict labor; or (3) to allow the importation of goods (or the release of goods on which there is in effect a detention order) mined, produced, or manufactured by forced or indentured child labor. (Sec. 517) Prohibits the use of funds in this Act to pursue or adopt regulations requiring airport sponsors to provide, without cost to the Transportation Security Administration (TSA), building construction, maintenance, utilities and expenses, or space for services relating to aviation security (excluding space for necessary checkpoints). Permits negotiations of below-market rates for these items. (Sec. 518) Prohibits the use of funds in this Act in contravention of the Buy American Act. (Sec. 519) Prohibits the use of funds provided by this or previous appropriations Acts for deployment or implementation on other than a test basis of the Computer Assisted Passenger Prescreening System (CAPPS II) until the General Accounting Office has reported to the Committees on Appropriations that: (1) a system of due process exists by which passengers considered to pose a threat may appeal their delay or prohibition from boarding a flight; (2) the underlying error rate of databases will not produce a large number of false positives that will result in a significant number of passengers being treated mistakenly or security resources being diverted; (3) the TSA has stressed-tested and demonstrated the efficacy and predictive accuracy of all search tools in CAPPS II; and (4) the Secretary of Homeland Security (Secretary) has established an internal oversight board to monitor the manner in which CAPPS II is being developed and prepared. (Sec. 520) Requires the Secretary, for FY 2004 and thereafter, to charge reasonable fees for providing credentialing and background investigations in the field of transportation. (Sec. 521) Directs the Secretary to research, develop, and procure certified systems to inspect and screen air cargo on passenger aircraft at the earliest possible date and to take certain preventive measures in the interim.