I think there is a great difference between the two. Project planning is a project management task that is very centric to PM and is usually done by the project manager (sometimes with the help of the project planner). Project planning is about determining the schedule and estimating the costs of the whole project, as well as planning the communication, accounting for risks and conflicts, etc...
Component planning, on the other hand, is a technical task that is about assessing how long (and costly) a component will take to be developed by breaking out the work on the component into manageable tasks (similar to a mini WBS). In the case of component planning, the costs, risks, schedule, conflicts, etc... are all restricted to the scope of the component, and not the project itself. The project manager will get the component plan from the component planner and will use it to build the project's schedule.
I hope I was able to clarify the differences between the two.