You can check on the D.O.T. website. They have a list of accepted vehicles and a list of registered importers. There is a mandatory test that vehicles have to go through. The cost is around $7,000 plus the cost of any modifications that have to be done to match U.S. specs. The modifications have to be made by the impoter. A vehicle can also be imported for show or display, but I never really checked into that.
http://www.nhtsa.dot.gov/cars/rules/import/