External Interrupts 89c51 using Keil Compiler

Hi ,
I want to use external interrupts of 89C51 to receive/transmit data using sync modem.
Following is the C code i have written but
that is not working.I'm using evaluation version of Keil Compiler . I have following
doubts about ISR in C
1. Do we need to enable and disable the interrupt in its ISR to prohibit it to interrupt
unless its ISR is over.
2. It it necessary to specify the register bank ( using 1 ..... etc )
3. To set serial port baud rate do we need to set TCON regs , default C51 setting is
sufficient or not.
4. Do I need to modify startup.a51 file for this code.

Can anybody suggest me any other way to control sync modem ( source code or any url ) ?

thaks
Sanjay

/*;Program to Transmit data to GMSK CMX469 Modem
;Int0 -> Applied RxSync clock   used for data sending P3.2
;Int1 -> Applied Txsync clock  used for data receiving P3.3
;P1.0 -> Tx data
;P1.1 -> Rx data
;P1.2 -> Carrier Detect
*/
#include <reg51.h>
#include <stdio.h>
//void ReceiveData(void);				//to be called by interrupt ISR
//void TransmitData(void);				//to be called by interrupt ISR

void InitializeInterrupts(void);
void InitSerialPort(void);
static void INT0_ISR (void);				//RX Sync clock
static void INT1_ISR (void);				//TX sync clock
void main()
{
 InitSerialPort();
 InitializeInterrupts();
  while(1)
   {   P0=0xff;   P2=0xff; }
}
static void INT1_ISR (void) interrupt 2 using 1                      //for tx
{
	EX1=0;   //disable int1
      P2=0x00;  // making it zero to know whether intr has ocured on falling edge
//	TransmitData(); 	//function to tranmit data
	EX1=1;   //enable int1
}
static void INT0_ISR (void) interrupt 0 using 1                          //for receive
{
	EX0=0;   //disable int0
      P0=0x00;  // making it zero to know whether intr has ocured on falling edge
		  //ReceiveData(); 	  //function to receive data
	EX0=1;   //enable int0
}
void InitializeInterrupts(void)
 {
		EX0=1;
		IT0=1;		//falling edge
		EX1=1;
		IT1=1;		//falling edge
		EA=1;
}
void InitSerialPort(void)
{
  SCON = 0x52;    /* SCON */                   /* setup serial port control */
  TMOD = 0x20;    /* TMOD */                   /* hardware (9600 BAUD @12MHZ) */
  TCON = 0x69;    /* TCON */
  TH1 =  0xfd;    /* TH1 */      //9600 baud rate
  TR1=1;
  printf("\nModem Program is running\n");
}