Making a field readonly in Catalog -> Manage Product -> General tab?

I have added a new field named category with开发者_开发知识库 a text box in Catalog -> Manage Product -> General tab, via the Manage Attributes and Attribute Sets tab. I want to make this field readonly. Please help me anyone. How can I do this, and tell me the page source.

Thanks

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solved that problem..by changing

app/design/adminhtml/default/default/template/catalog/form/renderer/fieldset/ele­ment.phtml file like

$_element = $this->getElement() ?> checkFieldDisable()

// START: My Change if((strpos(trim($this->getElementHtml()), '"categories"') !== false))

{

$_element->setDisabled(true);

} // END: My Change ?>