I am working on a project in After Effects 5.5 where I need the camera to zoom around 30,000 px in. My camera is starting at -4000 depth and works fine until I go from the negative to the positive px. When it gets to positive pixels the elements all reflect and look as though they are zooming out. A friend of mine is using AE 5 and she has no problem zooming in, infinitely. Is this a glitch or am I missing something?
Zoom is animated using the zoom property. It sounds like you keeping the focal length the same and moving the camera. This is called a dolly, truck, or camera move.
If you created a single axis camera or if you're moving both the camera and the point of interest then the camera will stay pointed in the same direction as you move it into the scene. If the point of interest remains at the comp center and 0z then when the camera passes zero z it will flip around a lock back at the point of interest.
Looking at the camera path from a top or side view you'll see the flip. This is normal behavior. You can fix it by auto orienting the camera to the camera path, using a single node camera, animating the point of interest, or using a null as a "dolly" for your camera and attaching the camera by parenting. The last option is how I animate cameras 99% of the time. It's the most versital solution.
My typical setup for animating a camera:
You're missing the point of interest stuff in your considerations, as Rick already said....