Making posts exclusive for just one category

Hi, this is my first contribution to wordpress-2.0.1 so I it functions.

I wanted to change my post form in a way that authors can only select one category for each post. What I did was to edit the admin-functions.php in the wp-admin folder. In this file look for this piece of code (line 560 for the 2.0.1 version):

function write_nested_categories($categories) {
<input value="', $category['cat_ID'], '" type="checkbox" name="post_category[]" id="category-', $category['cat_ID'], '"', ($category['checked'] ? ' checked="checked"' : ""), '/> ',

change the word “checkbox” for “radio” and that’s it!