Adding fields to the “Add New User” screen in the dashboard

user_new_form is the hook that can do the magic here.

function custom_user_profile_fields($user){
  ?>
    <h3>Extra profile information</h3>
    <table class="form-table">
        <tr>
            <th><label for="company">Company Name</label></th>
            <td>
                <input type="text" class="regular-text" name="company" value="<?php echo esc_attr( get_the_author_meta( 'company', $user->ID ) ); ?>" id="company" /><br />
                <span class="description">Where are you?</span>
            </td>
        </tr>
    </table>
  <?php
}
add_action( 'show_user_profile', 'custom_user_profile_fields' );
add_action( 'edit_user_profile', 'custom_user_profile_fields' );
add_action( "user_new_form", "custom_user_profile_fields" );

function save_custom_user_profile_fields($user_id){
    # again do this only if you can
    if(!current_user_can('manage_options'))
        return false;

    # save my custom field
    update_usermeta($user_id, 'company', $_POST['company']);
}
add_action('user_register', 'save_custom_user_profile_fields');
add_action('profile_update', 'save_custom_user_profile_fields');

For more details visit my blog post: http://scriptbaker.com/adding-custom-fields-to-wordpress-user-profile-and-add-new-user-page/