While you start using the Arduino and the Ethernet Shield, you probably noticed you can't change your Shield's ip, mask or gateway. This sketch will give you a small web page, where you can submit your values.
This sketch can't reset your Arduino, you'll have to do that yourself. What I can do, is save those values you submit in EEPROM and the next time your Arduino boots, it will use your new submitted numbers.
Also you'll have to change ip, mask and gateway the first time you'll use the sketch. the Sketch will know it's the first time it has ran and use those defaults only once. upload the sketch, open your browser and go to IP-address/setup
If you would like to comment, you can do so on the arduino forum in this post: http://arduino.cc/forum/index.php/topic,55044.0.html
Wondering about the webserver, check this: http://arduino.cc/en/Tutorial/WebServer
Asking yourself how the EEPROM library works: http://www.arduino.cc/en/Reference/EEPROM
You want to find out how to store data in flash (program) memory instead of SRAM: http://www.arduino.cc/en/Reference/PROGMEM
And finally you want to know more on the Text Finder Library, this should help: http://www.arduino.cc/playground/Code/TextFinder
EthernetSetup1.0: first release
EthernetSetup1.1: Solved dns problem. Now you can use Arduino IDE 1.0.3