Don't copy this. It's just a sample of doing it wrong.

wp-query-doing-it-wrong.php

<?php

/*
 * WP_Query doing_it_wrong
 *
 * i'm commenting this so you don't copy / paste this fail sauce
 */

$original_query = $wp_query; // YUDOTHAT???
$wp_query = null; // Oh, man

$args = array (
	'post_type'		=>	'post',
	'author'		=>	5 // these args can be whatever
);

$wp_query = new WP_Query( $args ); // you're killing kittens

if ( $wp_query->have_posts() ) {
	while ( $wp_query->have_posts() ) {
		$wp_query->the_post();
		
		// do stuff		

	}
} else {
	
	// aww, no posts... do other stuff
	
}

$wp_query = null; // ugh
$wp_query = $original_query; // sigh face

wp_reset_query(); // guess so. in a normal WP_Query, only wp_reset_postdata() is needed.