Why not using an oscilloscope to monitor the two signals on RX and TX.
I think it would be better than modifying your circuit (with all possible error that could cause)
you can monitor any one line at a time without any problem, just connect any one of the line (TX1 or TX2) to T1IN of max 232 and give its other end (T1 out) to PC. use hyper terminal to monitor the data.
if you draw a very simple schematic to illustrate what you are trying to achieve, it might make it easier for others to help you. Post the drawing here.
PIC#1 TX1 connect with PIC #2 RX2
PIC#2 TX2 connect with PIC #1 RX1
RS232 RX3(T1IN) should be connected with TX1 & TX2 to monitor PIC's data
RS232 TX3(R1OUT) should bbe connected with RX1 & RX2 to end data from PC to PIC's
Please check an attachment for your reference
Need a simple low cost less circuitry hardware for doing above task practically