using form_alter to amend field attributes - such as setting a default value

Originally I had been using a custom form rather than form_alter, but I had issues of compatibility with CCK.

I have the following code I'm working from:

<?php
function test1_form_alter(&$form, $form_state, $form_id) {

  switch ($form_id) {
    case 'kg_media_type_node_form':
      
      $form['field_kg_url'][0]['#weight']= -5;
      $form['field_kg_url'][0]['#default_value'] = $form_state['values']['field_kg_url'][0]['value'];

      $form['field_kg_title']['#size'] = 30;
      $form['field_kg_title']['#weight'] = -4;
      $form['field_kg_title']['#default_value'] = $form_state['values']['field_kg_title'];

      $form['title']['#required'] = false;
        
			$form['populate'] = array(
				'#type' => 'submit',
				'#value' => 'Retrieve info',
				'#validate' => array('test1_populate'),
				'#weight' => -4,
			);
      break;
  }
}

//---------------------------------------

function test1_populate($form, &$form_state) {

  $kg_url = $form_state['values']['field_kg_url'][0]['value'];
  
  $kg_page = get_kg_page($kg_url);
  $kgInfo = scrapeKGInfo($kg_page);
  
  form_set_value($form['field_kg_title'][0]['value'], $kgInfo['title'], $form_state);
  form_set_value($form['field_kg_url'][0]['value'], $kgInfo['kg_url'], $form_state);

  //previously before using a CCK type the following worked fine:
  //form_set_value($form['field_kg_url'], $kgInfo['kg_url'], $form_state);

  $form_state['rebuild'] = TRUE;
  drupal_set_message(t('KG info retrieved'));
}?>

What I'm trying to do is have a CCK type, add a button which when pressed, takes the value of a field (URL) and after doing some logic, populates the other fields using the data scraped from a page defined by the URL. So I need to do two things which I'm not able to do with CCK type fields:
- set default value
- set the value.

Are there functions I should be calling to set/get the values of CCK type fields?

Additionally once that is solved, for fields which can have multiple values (ie tags) how can I set such a field to have a multiple number of default values?

As far as title field goes, i was a) testing non cck fields (it works fine to change its attributes) and b) later on i'm going to set the title based on retrieved information....

Thanks!

Daz