MOSI and MISO at 89S52
No, you can't connect these pins to the PC serial port.  

The main reason is they are SPI pins, and you need to use the UART pins for this. The UART pins will be usually named RX and TX (though the datasheet will tell you)  

Secondly, the voltages from the PC serial port are incompatible with your chip, so you you need something like the MAX232 suggested by AndrejaKo to translate the levels.

I suggest doing the following:


Read the Wiki page on UART (linked to above) 
Read the datasheet - at the very least the UART section.       
Google for examples of using UART for your chip.


For the last point I did a quick google for "89S52 UART example" and got quite a few relevant pages back.
Here is some basic example code for the UART from one of them:  

#include &lt;REGX52.h&gt;
#include "delay.h" 
#include &lt;stdio.h&gt;        
unsigned char temperature; 
unsigned char humidity; 
void uartInit(void) 
{ 
 SCON  = 0x52;            
  TMOD  = TMOD|0x20;         
 TH1   = 0xfd;           
 TR1   = 1;        
} 
void main(void) 
 { 
  uartInit(); 
  for(;;) 
  { 
    printf("Temperature : %bu  Humidity : %bu \n", temperature++, humidity++);
    DelayMs(1000); 
  } 
} 


EDIT - to use the SPI pins to connect to a PC, you need the PC to have an SPI capable interface (which don't come as standard on most machines) To add one you will need an SPI host adapter like this which can be plugged into the PCs USB port.