/3/ - 3DCG

Anyone know of a good way to make an object follow a curve, but only lock it to one axis?
Like in the example, I'd want the monkey to stay a fixed distance from the camera, but also follow the curve left and right.
I had figured I could just animate the path, and then make the monkey follow the curve at the same speed (so the speeds would match), but it doesn't work like that apparently.

I have to keep the camera fixed in this, otherwise I'd just follow the monkey without any problems. I could always hand animate the motion as well, but I'd like to have it follow a curve so it's not as messy.