Here is the area where GtkAssistant and GnomeDruid differ the most. While GnomeDruid used the "next" and "back" signals from the GnomeDruidPage, GtkAssistant uses the following techniques:

A sample GtkAssistantPageFunc could look like this:

static gint
forward_page_function (gint     current_page,
                       gpointer data)
{
  switch (current_page)
    {
    case 0:
      return 1;
    case 1:
      if (check_page1_data ())
	   return 2;
	 else
	   return 3;
    case 2:
      return 3;
    default:
      return -1;
    }
}