Alter the $content variable with a module or template.php

Hello Drupalers,

I feel I'm making a lot of headway into drupal theme and module development, but still have brain explosions when trying to follow best practices.

I have created a module that will display a node's listed attachments in a block in the sidebar.

Drupal's built in upload module is set-up to display these attachements at the bottom of $content in a node. And I want to remove it again.

line 270 of upload.module

function upload_nodeapi(&$node, $op, $teaser) {
  switch ($op) {
  .
  .
  .
    case 'view':
      if (isset($node->files) && user_access('view uploaded files')) {
        // Add the attachments list to node body with a heavy
        // weight to ensure they're below other elements
        if (count($node->files)) {
          if (!$teaser && user_access('view uploaded files')) {
            $node->content['files'] = array(
              '#value' => theme('upload_attachments', $node->files),
              '#weight' => 50,
            );
          } 
        } 
      }
      break;

I know I could create a node.tpl.php file removing $content and listing the required items, but wanting to improve my drupal skills and edit $content using a module or template.php. Ideally I remove the [files] from the $content in my custom module.

I hope that makes sense.

The code for my custom module (site_custom.module):

/*
 * Implementation of hook_block()
 */
function site_custom_block ($op = 'list', $delta = '0', $edit = array()) {
	switch ($op) {
		case 'list' :
			$blocks[0]['info'] = t('Attachments');
			return $blocks;
		case 'configure':
			return;
		case 'save':
			return;
		case 'view' :
			$nid = print_r(arg(1), True);
			$files = upload_load(node_load($nid));			
		$rows = array();
		  foreach ($files as $file) {
		    if ($file->list) {
		      $href = $file->fid ? file_create_url($file->filepath) : url(file_create_filename($file->filename, file_create_path()));
		      $text = $file->description ? $file->description : $file->filename;
		      $mime = strtoupper(substr($file->filemime, strrpos($file->filemime, '/')+1));
		      $header = array(t('Format'), t('File'), t('Size'));
					$rows[] = array($mime, l($text, $href), format_size($file->filesize));
		    }
		  }		
		  if (count($rows)) {
		    //$block['content'] = theme('table', $header, $rows, array('id' => 'attachments'));
				$block['content'] = theme_table($header, $rows, array('id' => 'attachments'));
		  } 			
		return $block;
	}
}

And for a bonus point:
What's the difference between

What is the difference between:

$block['content'] = theme('table', $header, $rows, array('id' => 'attachments'));

and

$block['content'] = theme_table($header, $rows, array('id' => 'attachments'));