Question: There is a function in Drupal 5 (`_phptemplate_variables()`) that has been deprecated in Drupal 6.
Is there a similar function in Drupal 6?

Answer: 
well, i'm not totally sure what you mean, but according to the title of the post, you want a redirect function ?

something like the drupal\_goto(); function?

<http://api.drupal.org/api/drupal/includes--common.inc/function/drupal_goto/6>
`_phptemplate_variables()` is not a function that has been deprecated. It is simply a private function that is not used anymore.

Drupal 5 PHPTemplate engine looked for a function with that name to alter the variables used in a template.

```
function _phptemplate_callback($hook, $variables = array(), $suggestions = array()) {
  global $theme_engine;

  $variables = array_merge($variables, _phptemplate_default_variables($hook, $variables));

  // Allow specified variables to be overridden
  $variables_function = '_'. $theme_engine .'_variables';
  if (function_exists($variables_function)) {
    $variables = array_merge($variables, call_user_func($variables_function, $hook, $variables));
    // …
  }
  // … 
}

```

What the code for Drupal 6 needs to do is to implement `MODULE_preprocess(&$variables)`, or `MODULE_preprocess_HOOK(&$variables)` (where `HOOK` is `page`, `node`, `comment`, or any of the values defined from a theme or module).