I see no problem you have to face in your setup. The PC SW will know nothing about nature of RS232 port it will use. It can be a real RS232 or Virtual one via USB adapter unless you are using real time bit banging with pins of RS232 port. If you are just sending data bytes there should be no difference between UART based or Virtual COM port.
I still do not get what is the task and what is the final goal of your project?
Is it communicating with PIC from PC via RS232?
In this case why should it be C++ Builder and why should you write any SoftWare at all? Here is the easier way:
This board is USB to RS232 (and SPI,I2C,...) adapter.
You connect it to the PC USB port and take it's RS232 output and connect it to PIC.
SUB-20 software has a GUI utility to send and receive data via RS232
BTW there is a chance you will not need PIC at all. Look over SUB-20 interfaces and perhaps it will totally suite your needs.
All of the interfaces are controlled via GUI application.