Need a bit of help with generating checkboxes, submits

The forms API is great - it just takes a bit of getting used to. But I've not yet found anything I couldn't do with it.

As for how to put your checkboxes in a table, you have to run it through a theming function:

<?php
function mymodule_form($form_state)
{
  $rows = db_query("SELECT nid, title, created {node}"); // this is a typical query from the node table to get some info about nodes
  while($row = $rows) // we loop through the results
  {
    $checkboxes[$row['nid']] = ''; // a blank value is given so that the checkboxes have no title and are just rendered as a blank checkbox
    $form['data_table']['title'][$row['nid']] = array("#value" => $row['title']); // we key each of the rows by the checkbox NID. If you aren't using NIDs, make sure that the checkbox　values are unique. If they aren't, then you need to use some other key to make sure that each row is unique
    $form['data_table']['created'][$row['nid']] = array("#value" => $row['created']);
  }
  $form['data_table']['nids'] = array // now we put the checkboxes into the form
  (
    '#type' => 'checkboxes',
    '#options' => $checkboxes,
  );
  $form['data_table']['#theme'] = 'mytheme'; // here we call the 'data_table' section of the form to themed using the theme 'my_theme'
  // do the rest of your form definition here
}

function mymodule_theme() // here we register our theme functions (or templates)
{
  return array
  (
    'mytheme' => array // this is the name of the theme we want to register
    (
      'arguments' => array('form' => NULL), // we pass it one value - form. This will be the 'data_table' section of $form from the form API function
    );
  );
}

function theme_mytheme(&$form) // now we declare our theme function
{
  $has_posts = isset($form['title']) && is_array($form['title']); // first we check to see if any values (rows) were actually passed to the function to be themed.
  $select_header = $has_posts ? theme('table_select_header_cell') : ''; // if there are posts, we add a checkbox to the header. This checkbox will be a 'check all' checkbox - when a check is entered into it, all checkboxes get checked. If there are no posts, then we enter nothing
  $header = array($select_header, t('Node Title'), t('Created On')); // this is the header for our table. It's got three columns - one for the check all box, one for the node title and one for the creation date
  $output = ''; // here we initialize a blank row

  if ($has_posts) // if we have posts, we start to build our table. We need to build an array called $rows. Each element of this array will be one row of the table (see http://api.drupal.org/api/function/theme_table/6 for more information on building tables in Drupal)
  {
    foreach (element_children($form['last_name']) as $key) // this gives us the unique index that we keyed each of our rows by in the while loop in the form definition
    {
      $row = array(); // we initialize a blank row. All the row data will go in here
      $row[] = drupal_render($form['nids'][$key]); // drupal_render renders the API definition, which is an array, into a proper form element. This will be the checkbox
      $row[] = drupal_render($form['title'][$key]); // this is the node title
      $row[] = drupal_render($form['created'][$key]); // this is the node creation date
      $rows[] = $row; // here we add the array that is that row to the $rows array
    }
  }
  else
  {
    $row = array('data' => t('No rows were found'), 'colspan' => 3) // this is a default message when no rows are found
    $rows[] = row;
  }
  $output .= theme('table', $header, $rows); // this builds our table
  $output .= drupal_render($form); //this calls some last rendering functions on the 'data_table' section of the $form from the form definition in the original function
  return $output; // and now we return our themed section of the form. This will be rendered in a table.
}
?>

There you go. It's not the easiest thing to do, but it works really well and you end up with a nicely formed table that will have a sticky table header if the form is longer than can fit into one screen. See theme_table() at api.drupal.org for more info on building HTML tables in Drupal.