You'll want to try to troubleshoot things and see where the problem is then.
The one thing I should have told you is that you'll need to go into your Arduino code and look at the pin assignments I have for the servo motors. I'm sure your servos aren't connected to the same pins so you'll need to modify the arduino code so that it is specific to your configuration.
Also, I modified my servos for continuous rotation. I just experimented with values to use to get the wheels to turn in the proper direction. Those values in my code may very well not work with your servos but they should at the least move somehow through that php code.
If all that doesn't work I'd ask:
Have you successfully read serial data on your arduino to do something simple like light up an LED or anything?
When you press the buttons...do you get the status messages appearing above the buttons "Forward signal sent" or something along those lines? That would indicate that the php code is working correctly?
Did you install WampServer?