I spent many many hours trying to piece together enough info to be able to control my arduino over via usb serial via a web page. I will outline the steps to hopefully help some one else !
Keep in mind this is all for Mac, specifically osx 10.6
enable PHP and apache
get the php serial class script
Scroll down to "Project Name: Arduino Serial LED Via PHP"
modify the serialledcontrol.php file for your baud rate and your communication port address
these 2 lines...
$serial->deviceSet("/dev/cu.usbserial-A4001234"); //SET THIS TO WHATEVER YOUR SERIAL
$serial->confBaudRate(9600); //Baud rate: 9600
The lines such as these actually determine what data is being sent
Put serialledcontrol.php and php-serial.class.php in the /user/Sites/ folder
The arduino should now receive the characters sent from the serialledcontrol.php
Also I have the arduino serial monitor open and you can see responses in the serial window!
There was talk that the arduino may reboot before/during/after the serial port opens/closes ... I cant confirm at this time ...