I recommend first off reading up on the Ethereal Plane (http://dnd-wiki.org/wiki/SRD:Ethereal_Plane).<br/><br/>As you'll note, there's no 50% chance. That's only for incorporeal creatures.<br/><br/>No magic passes between the two, except for force effects cast on the material plane, and those automatically work.<br/><br/>Second, that doesn't affect any spells that you cast on yourself or someone else on the same plane as you. So it would work no problem.