I have an S10 reg cab and can't get the visor clips out nor can I remove the front post.

There are no clips that hold the visors - they are held in place by screws. You can view an online guide to removing and replacing the S-10 or Sonoma headliner by going to this link: S10 or Sonoma headliner replacement. It will give detailed instructions on removing, recovering and replacing the headliner in your Chevy S10 standard cab truck.