Mouse Movement

I recently downloaded the source code to the old player world (mirage) game engine. I am trying to tinker with it to try some new features. I am trying to get it so that the player moves by mouse click instead of just using the arrow keys. I want the player to move to the location of the mouse click. Unfortunately my efforts havent worked out too well. The player does move but he runs off the screen and wont stop for some reason. Keep in mind I am doing this using DirectX drawing the player inside a picture box. Any ideas/suggestions/code would be greatly appreciated. Thank you for your assistance.