When you say 473 do you mean 473 ohms (unusual value, but possible if it is a high precision resistor) or does the resistor have 473 written on it (which could mean 47000 ohms)? If you are unsure, check it with a multimeter.For V and H sync just experiment, the value shouldn't be too critical, try whatever resistors you have between 10 ohms and 100 ohms.Are the monitors LCD or CRT? Both should work, though LCD monitors can sometimes be a bit random.
Are you shure that the Arduino Mega cant handle it
Can the arduino handle two different codes to the same time?