Sorry, I was just demonstrating that you can squeeze a lot of html output on to a 328.
If I understand what you are asking.
If you want forms and form handlers on the arduino so you can pass actions or commands over to be handled by the arduino. Its just a matter of handling the request in code on the arduino.
You can capture and interpret the value pairs passed in the query string.
So for example:
http://myipaddress?led=on
In the request look for the value pair led=on and turn on an led.
This request could either be entered by you on the address bar of a browser or as a result of a web page containing a form that was served up by the arduino.
Theres are some simple examples with the nuelectronics ehternet boards.
http://www.nuelectronics.com/estore/?p=12.
They wont work with the Arduino Ethernet board but you canget some ideas on how to do it by adapting there code to work with the arduino board.
Gordon