http://kevin.org/frc/
Kevin has serial port routines, that should get the serial port on the RC working. It doesn't really matter if you use parallel or serial interface, once you get it transparent to you, so that all you do is tell it to send the byte, and it doesnt matter how it gets sent.
A lot of the microcontrollers have onboard serial ports, with hardware control, and some have more than one... as you see with the 18F that is in the RC.
As for the code for the other processor, you have to know what you are going to do with the processor before you worry about that.