I just finished toying with some HTML GET/ commands (Commonly used in Arduino web servers to send text to an lcd through a web interface.) and I quickly realized how difficult this would be.
I'm sure there is another way to do all this, but currently, I am at a stand still.
I'm still open to Ideas though.
If you want to do it over the HTTP interface, you'd conventionally use an HTTP Post request with the data you're submitting containing the new page content and associated parameters. If your Arduino is connected to a PC too, you have the option of sending the page update request over the serial link, for example as a sequence of S records.