How can I make my pointer move at a constant rate versus my mouse?

When you move an external mouse slowly, the pointer moves very slowly, and when you move it quickly, it the pointer moves very quickly. This sounds intuitive, but the tracking speed is not proportional to the mouse movement. I need the mouse and pointer to move at a 1 to 1 when using programs like Photoshop. How can I disable this "helpful" mouse speed acceleration/deceleration?