Originally Posted by RoadGuy

Using vice grips can be self-defeating. When you tighten the jaws, you are crushing the nipple body onto the spoke threads, making it harder to unscrew the broken nipple. . . . QUOTE]

Or, you can rotated the nipple 90 degrees in the vise grip, crush it again, and just remove the now more broken (preferably in half lengthwise) nipple. You might have to do it a few rotations, but brass is soft, and like a paper clip, will break eventually.The spoke should still be good if you didn't "Over Crush". Then you just replace the nipple and true the rim.