If you can watch a video of Lew Sterrett "round penning" a young or untamed horse, it will help you a lot. ( www.sermononthemount.org
) . Basically what he does is very similar to what Saddlebag suggested. He gently encourages the horse to keep moving (doesn't have to be fast) around the round pen (or small paddock). The instant that the horse turns his head and looks at him with both eyes, Dr. Lew looks away and turns away from the horse, removing all pressure. Brief pause, then repeat. Pretty soon the horse realizes that if he moves away from the handler, he has to keep working (moving), but when he stops and turns TOWARD the handler, he gets to rest. It really doesn't take long to get the horse to want you to walk up to him and pet him.
I had the opportunity to try this with my own horse last summer, when he decided he didn't want to be caught by me. He was in a small paddock, so I just kept him moving and moving until he wanted to stop on his own. As soon as he did and turned toward me, I stopped pushing him to move and turned and walked away from him. I only had to do it a few times before he was following me all over the paddock.