If you want to send data serially to MATLAB, you can use the functions in RS232.LIB. Take a look at Samples/SERIAL/PUTS.C for a simple example of sending a string out on serial port B.
The POT and IR sensor sound like they might be analog devices? Are you using a Rabbit module with an ADC to convert analog readings?
I recommend exploring the sample programs and using samples as starting points for various pieces of your application. Work on code to read the POT and IR sensor, then code to format the data in a way that MATLAB can process it, and then add in the code to send it over the serial port.