The SCOTUS ruled after congress gave clinton a line item veto (that he used exclusively to veto tax breaks -- never once to veto a spending item) that the Constitution did not allow for a line item veto. Therefore, it would take more than Congress to approve a line item veto; it would take two-thirds of both houses of congress and then ratification by the legislatures of three-fourths of the states.
Yeah. So what is Bush's talk about getting a line item veto? It is a bunch of hogwash and just an excuse by him to keep signing off on spending.