There are two 'built-in' ways of doing this in Wordpress:
1) If you need access to the link as a PHP variable, try Using get_next_posts_link
<?php $nextLink = get_next_posts_link( $label , $max_pages ); ?>
<?php $previousLink = get_previous_posts_link( $label ); ?>
From here the links are stored in variables and you can do whatever you'd like with them.
2) Otherwise use these:
<?php next_posts_link( $label , $max_pages ); ?>
<?php previous_posts_link( $label ); ?>
Where $label is the name of the link ( "Next Page" in your case ) and $max_pages is the max number of pages (if you want a limit), that the link shows up on.
If you want to style these, without having to enclose them inside another DIV, use Wordpress Filters
function apply_my_next_link_style ( ){
return 'class="button"';
}
apply_filters( 'next_posts_link_attributes', 'apply_my_next_link_style' )
3) If you need even more control you can try this, from the source code for the above functions:
if ( !is_single() ) {
echo '<a href="' . next_posts( 0, false ) . "\" $attr>" . preg_replace('/&([^#])(?![a-z]{1,8};)/i', '&$1', "Next Page") . '</a>';
}
Also, I would suggest asking these types of questions over at wordpress.stackexchange.com
