How to use a field value in Template.php
You can find the node object in $variables['node'], and from there you can use the field_get_items() function to extract your field value:

$node = $variables['node'];

// field_get_items() always returns an array, even if the field is limited to one value
$field_items = field_get_items('node', $node, 'field_name');

// Get the value from the first item in the array (if that's the one you need)
$title = $field_items[0]['value'];