glUnProject...?

I have created a ball (glutSolidSphere(1)) and I want to destroy it by clicking with the mouse, and then I have to convert x,y to the world coordinates, and if I’ve got it right I should use glUnProject, but I can’t get it to work because the ball is about 1/10 of the width of the screen, but when I click I can only get float values from 0 to 1, and it doesn’t matter if I change the far (Z) variable in glUnProject…

If anyone got something of this mess, plz reply…

Thanx…