OpenGL selection problem

I am making a hair modeliing demo. I load a face geometry in triangles. I use openGL picking and depth values example 13.6 of programming guide book. I orbit the camera with gl''s rotate function. Works ok for the triangles, but after i add the hair i cannot select correctly the hair strands or points. It finds i suppose the depth value of the hairs and points and makes the mistake? Does anybody know how to achieve this? Also how can i possibly implement a rect selection tool? Is there any tutorial about it? Thanks