1. A method for determining the best entry point for a percutaneous procedure, given a primary target for biopsy and a secondary target through which a biopsy needle must pass on its way to said primary target, comprising: selecting a first arbitrary entry point on a patient; selecting a second arbitrary entry point on said patient, different from said first arbitrary entry point; determining the three dimensional (3-D) orientation of said needle at said first arbitrary entry point for pointing said needle at said primary target; determining the 3-D orientation of said needle at said first arbitrary entry point for pointing said needle at said secondary target; determining the 3-D dimensional orientation of said needle at said second arbitrary entry point for pointing said needle at said primary target; determining the 3-D orientation of said needle at said second arbitrary entry point for pointing said needle at said secondary target; determining a 3-D line representing the intersection of a first plane containing said first arbitrary entry point, said primary target point, and said secondary target point, and a second plane containing said second arbitrary entry point, said primary target, and said secondary target point, whereby said 3-D line provides a position and orientation for said needle for performing needle biopsy of said primary target through said secondary target.