You are talking about two different technologies. The interface method you are talking about is using one of the PICs USARTs to communicate with another PIC. The method that you referenced from the data sheet is using SPI and the PICs MSSP to communicate with another PIC.
To talk to the RC you will need to use the USART. I just want to be sure - are you trying to interface an RS-232 level port from your demo board with the TTL port on the RC or with the RS-232 level port (Program Port) on the RC? Unless you want to use a level shifter like a MAX232 you probably want to use the RC's Program Port to communicate with your demo board. Also, SPI communication with either of the PICs on the RC is not possible because IFI has used the SPI ports to link the Master with the User.
If you are using the C18 compiler you might want to take a look at the
sample code that Kevin Watson did demonstrating serial communication with the RC. I think you'll have to modify the code if you are using a PIC that only has one USART (like the 452).