как-то так, наверное
<a href="" id="id_button_prev">назад</a>
<a href="" id="id_button_next">вперед</a>
<script>
var urls = [
'http://url_1',
'http://url_2',
'http://url_3',
'http://url_4',
'http://url_5',
'http://url_6'
];
for (var i = 0, currentUrl = window.location, len = urls.length; i < len; i++) {
if (currentUrl.indexOf(urls[i]) {
if (i > 1) document.getElementById('id_button_prev').href = urls[i - 1];
else document.getElementById('id_button_prev').style.display = 'none';
if (i < len - 2) document.getElementById('id_button_next').href = urls[i + 1];
else document.getElementById('id_button_next').style.display = 'none';
}
}
</script>