I cant believe I am asking this question...

I'm gonna get laughed right outta the forums I know it, but I've never tried to do this before. How would I position a sphere to the mouse, and move it with the mouse, but just on the x axis. Trust me, I have looked all over the site before I asked this embarrasing question.

MoveMouse GraphicsWidth/2,GraphicsHeight/2
MoveEntity Sphere,MouseXSpeed,0,0

Which x axis are we talking about here? 3D global, 3D local to the sphere, or the screen's x axis?