Thanks Nicusor: Works great. I was able to change the width of selected columns on the Posts panel (e.g Title, Author, Categories) with your solution as follows:
add_action('admin_head', 'my_admin_column_width');
function my_admin_column_width() {
echo '<style type="text/css">
.column-title { text-align: left; width:200px !important; overflow:hidden }
.column-author { text-align: left; width:100px !important; overflow:hidden }
.column-categories { text-align: left; width:100px !important; overflow:hidden }
</style>';
}