Custom node type that spits out a multi-page article

First of you may want to look at the paging module. If that is not what you have in mind, If you have written a module, you can achieve what you want in the view hook, if you used CCK you will need to do it in the template. Not knowing how you have organized your content I can only given you general pointers. Part of achieving your goal will be navigation aids above and/or below the content so users can move through the pages. As an example, lets say you have created an instance of this content and it node id is 12. From page 1 you can only move foward so lets say the forward link is node/12&page=2, on page 2 (given there is a page 3) would have a backlink of node/12&page=1 and a forward link of node/12&page=3.

The view hook or template would then need to determine the page it is on, something like this

if ( isset($_GET['page']) ) {
  $page = $_GET['page'];
  // You might want to range check page and
  // if out of range force it back in
}
else {
  $page = 1;
}

Then in general terms the whole code for view the content would look something like

if ( isset($_GET['page']) ) {
  $page = $_GET['page'];
}
else {
  $page = 1;
}
$max_page = ??;  // You need to determine this based on your content

// Output fields common to all pages

// Use $page to determine the page specific part(s)

// Here we put the navigation at the end, it could be in it's own theme function
if ( $page > 1 ) {
  $prev_link = l(t('Previous page'), "node/$node->nid", array(), 'page=' . ($page-1));
}
if ( $page < $max_page ) {
  $next_link = l(t('Next page'), "node/$node->nid", array(), 'page=' . ($page+1));
}
// Print the prev/next links with html approriate to your needs.