Ahmed, the .5 ohm resistor is used to control the current to your motors. Your motors won't run because 5 ohms will give you only 200ma of current (if I'm not mistaken). You need to look in the L297 data sheets to see what value you need for 1.6 amps. I think it has to be .62 ohms.
The voltage does not matter much, since the controller will do the current limiting. Generally the higher the better, but don't exceed the rating of chips.
I think you might have trouble with resonance because the circuit does not have microstepping. If you want to get full performance out of your motors, you should use a different circuit. Check out Phil's a3977 board in the open source forum.