Clean Air Incentive Act of 2003 - Amends the Internal Revenue Code to allow a limited credit for qualified ozone attainment vehicle property. Defines such property as any qualified clean-fuel vehicle property, if substantially all of the use of such property is in an area designated as either: (1) a serious ozone nonattainment area; (2) a severe ozone nonattainment area; or (3) an extreme ozone nonattainment area.