<?php if (is_front_page()) { ?>
    <div class="header-search">
        <form id="searchform-header" method="get" action="<?php echo get_option('home') ?>/">
        <input type="text" value="Search" name="s" id="s-header" onfocus="if (this.value == 'Search') {this.value = '';}" onblur="if (this.value == '') {this.value = 'Search';}" />
        <input type="submit" value="Search" id="search-button" />
        </form>
    </div>
 <?php } ?>