http://acquia.com/blog/migrating-drupal-way-part-i-creating-node
* also note that node_delete(nid) will delete a node.
<?php
// Construct the new node object.
$node = new stdClass();
// Your script will probably pull this information from a database.
$node->title = "My imported node";
$node->body = "The body of my imported node.\n\nAdditional Information";
$node->type = 'story'; // Your specified content type
$node->created = time();
$node->changed = $node->created;
$node->status = 1;
$node->promote = 1;
$node->sticky = 0;
$node->format = 1; // Filtered HTML
$node->uid = 1; // UID of content owner
$node->language = 'en';
// If known, the taxonomy TID values can be added as an array.
$node->taxonomy = array(2,3,1,);
node_save($node);
?>
(from the url listed above, article provided by Acquia)
Using the Devel module
The Devel module is a great way to see, among other things, the structure of the node object which is invaluable in this case. After installing the module and viewing a node you will see new tabs: Dev load and Dev render. Click the Dev load tab, then click the "... (Object) stdClass" header to expand the node object definition. Here you will find some familiar data like nid, type, etc. Near the bottom, you will see some other definitions that begin with "field_". These should resemble the CCK fields that you created for your node type.
Depending on your CCK definitions, the assignments in your import script might look like one of the following:
Here you can see some examples of how CCK has added fields to the node object
<?php
$node->field_text_field[0]['value'] = "value 1";
$node->field_text_field[1]['value'] = "2nd value";
$node->field_nodereference[0]['nid'] = 58;
?>
Add these assignments to your import script and you will start to see the power of the Drupal API. Let's say you are migrating from another CMS with a number of related fields, categories, images, etc. You could expand this script to iterate through your old database and map all of the related elements to a corresponding node object. Execute your script, and all of your old data will now become Drupal data! The best part about using the API is that it takes care of all of everything from search indexing to path aliases and all of the other little things we might overlook.
Migrating to Drupal can seem like a daunting task, but when doing things the Drupal way it's quite straight forward. Whether you are planning a migration of 100 nodes or 100,000 nodes, proper scripting can make it seem like a breeze!