利用两个普通的IO口作为按键接口就行了，我大致写了个程序，不知合不合你的要求：
#include "reg51.h"
#define uchar unsigned char
#define uint unsigned int

sbit rs = P3^5;
//sbit rw = P2^6;
sbit en = P3^4;
sbit key1=P3^6;
sbit key2=P3^7;

unsigned char code str1[]={"2011-04-13"};
unsigned char code str2[]={"WANGHAIMING!"};

void delay_1ms(unsigned int xms)
{
unsigned int i,j;
for(i=0;i<xms;i++)
     for(j=0;j<110;j++);
}

void wr_com(unsigned char com)  //写指令
{
delay_1ms(1);
rs=0;
//rw=0;
en=0;
P0=com;
delay_1ms(1);
en=1;
delay_1ms(1);
en=0;
}

void wr_dat(unsigned char dat) //写数据
{
delay_1ms(1);
rs=1;
//rw=0;
en=0;
P0=dat;
delay_1ms(1);
en=1;
delay_1ms(1);
en=0;
}

void lcd_init()
{
delay_1ms(15);
wr_com(0x38); delay_1ms(5);
wr_com(0x08); delay_1ms(5);
wr_com(0x01); delay_1ms(5);
wr_com(0x06); delay_1ms(5);
wr_com(0x0c); delay_1ms(5);
}

void displcd(unsigned char *p)
{
while(*p!='')
{
  wr_dat(*p);
  p++;
  delay_1ms(1);
}
}

void keyscan()
{
  uchar keynum=0;
   if(key1==0)
{                       
delay_1ms(5);
if(key1==0)
  {
   keynum=1;
  }
  while(!key1);
}
if(key2==0)
{
delay_1ms(5);
if(key2==0)
  {
   keynum=2;
  }
  while(!key2);
}

   switch(keynum)
   {
     case 1:wr_com(0x01);wr_com(0x80);displcd(str1); break;
     case 2:wr_com(0x01);wr_com(0x80);displcd(str2); break;
   }
}


void main()
{
lcd_init();
wr_com(0x80);
displcd(str1);
while(1)
{
keyscan();
}
}