The connector is called a DE-9.

The PC transmits on pin 3 and receives on Pin 2. Pin 5 is the ground.

Connect PC TX to 8052 RX, using a rs232 voltage converter such as max232 or max202, and PC RX to 8052 TX also using a voltage converter.

You will also need to be able to connect PDEN to gnd during reset to be able to initiate IAP after your program has been downloaded. There is a way in software to do this without the switch, but your question indicates you will be needing the switch.