What is the difference between all the Presbyterian churches.

Like PCA, OPC, and so on. I see some here are OPC, and some PCA, why the difference? I really dont know. How far apart is their theology?

As you can tell I am a Baptist and there are about 500 difereing Baptists and Baptist like denoms out there. I know there is the PC-USA wwhich I understand is completely heretical. But what of the OPC and PCA and so forth?

Thanks.

[Edited on 3-18-2004 by A_Wild_Boar]