linux web server to serial arduino

What would be the easiest method to set up a website that I can access atleast on the local internet, that would run on a small computer that would take commands in like an html text box or buttons and communicate to an arduino.
I got the arduino part done, however I have very little html or webserver knowledge and I couldn't even make a text box if I tried.
Im half decent at processing, so if there was a simple program to pass data to processing from a html client that would be awesome
any sugesstions would be greatly appreciated, especially free or cheap ideas lol

The apache web server might run on a linux box.

A few years ago, I used one of these (which is actually overkill)...
http://www.via.com.tw/en/products/embedded/artigo/a1000/index.jsp
...running Windows XP and Apache as a small web server.

Apache is definitely what I would use for the web server. I used Windows XP because my employer has a site license for the Windows operating system.

without using an ethernet shield youd need to use the serial port and you can do that from inside a webpage using php or python (probably you can do it with other languages too)

for php you can use this class PHP Serial: Communicate with a serial port - PHP Classes (if you need help writing the code give me a pm i can help you - just tell me what you need)
for python i dont have an example because i never used it in such ways but i know it can be done (cause it ca display webpages also play with the serial connection)