Tile Based Collision Detection

I am following Tonypa’s Tile Based Tutorials and I have to say, they are great. His covers everything needed, except for one thing - Refering to Tutorial 9, http://www.tonypa.pri.ee/tbw/tut09.html, Stupid Enemy, I want to make this a NPC in stead of an enemy. So what do I do to make it so that I don’t walk right over the enemy/NPC? I am trying to develop an RPG, and it would look silly to have the character walk on top of the NPC. Can someone provided a snippet on how to make a collision detection with the NPC and not walk on top/under the NPC?

One last favor to ask: What if I want to talk to the NPC if I am within a half tile? Would anyone be willing to share info on how this as well?

Thanks a bunch in advance