question on how can I disable form_input area?

[eluser]Nano HE[/eluser]
Hello.

How can I do this?
I want only disable one input area in my form.
And show some alert contents in the disabled form instead.

Code:

$data = array(
              'name'        => 'keyword',
              'id'          => 'searchform',
              'value'       => '',
              'maxlength'   => '100',
              'size'        => '25',
              //'style'       => 'width:20%',
            );

    echo form_input($data);

and the webpage viwed like this,
Like this: [Disabled Search for Traffic Limitation]