can anyone help me with prgraming the DFRobot 4WD Arduino Mobile Platform?

Thank you for your support, but it seems i have run into yet another problem. The back and front motors are driving away from eachother, even though i connected the right side motors and left side motors into different terminals. If anyone can explain what I am doing wrong I would be quite thankful.

here is the code i am using to control the rover using a keyboard:

int E1 = 4; //M1 Speed Control
int E2 = 7; //M2 Speed Control
int M1 = 5; //M1 Direction Control
int M2 = 6; //M1 Direction Control

///For previous Romeo, please use these pins.
//int E1 = 6; //M1 Speed Control
//int E2 = 9; //M2 Speed Control
//int M1 = 7; //M1 Direction Control
//int M2 = 8; //M1 Direction Control

//When m1p/m2p is 127, it stops the motor
//when m1p/m2p is 255, it gives the maximum speed for one direction
//When m1p/m2p is 0, it gives the maximum speed for reverse direction

void DriveMotorP(byte m1p, byte m2p)//Drive Motor Power Mode
{

digitalWrite(E1, HIGH);
analogWrite(M1, (m1p));

digitalWrite(E2, HIGH);
analogWrite(M2, (m2p));

}

void setup(void)
{
int i;
for(i=6;i<=9;i++)
pinMode(i, OUTPUT);
Serial.begin(19200); //Set Baud Rate
}
void loop(void)
{
char val = Serial.read();
if(val!=-1)
{
switch(val)
{
case 'w'://Move Forward
DriveMotorP(0xff,0xff);
break;
case 'x'://Move Backward
DriveMotorP(0x00,0x00);;
break;
case 's'://Stop
DriveMotorP(0x7f,0x7f);
break;

}
delay(40);
}

}