PHP4 upload handler

Util.php

<?php

class Bumpslide_Util 
{
    
    static public function CreatePath( $path ) {
        $folders=explode('/',$path);
        $existingPath= (($os = getenv('OS')) && (substr_count($os, 'Win')>0)) ? '' : '/';
        foreach($folders as $folder){
            if($folder=='') continue;
            if(!file_exists($existingPath.$folder)){ @mkdir($existingPath.$folder); }
            $existingPath.=$folder.'/';
        }
        if (file_exists($path)) return true;
        return false;
    }
    
    /**
     * Store an uploaded file to a unique folder within the upload path
     *
     * Return path relative to provided upload path.
     */
    static public function ProcessUpload( $file, $upload_path, $sub_folder='', $folder_date_format='Y-m', $memory_limit='500M', $time_limit=20 ) {
         
         ini_set('memory_limit', $memory_limit);
         set_time_limit($time_limit);
         
         if($sub_folder=='') $sub_folder =  md5( time() . $file['tmp_name'] );
         
         // sanitize upload path (no final /)
         $upload_path = dirname( $upload_path.'/.' );         
         $path = sprintf('%s/%s/%s/', $upload_path, date( $folder_date_format ), $sub_folder );
         
         if(!self::CreatePath( $path )) {
             throw new Exception('Unable to create upload folder: '.$path );
         } elseif ($file['error'] != UPLOAD_ERR_OK) {
             throw new Exception( self::UploadErrorMessage( $file['error'] ) );
         } else {

             $temp_file = $file["tmp_name"];
             $saved_file = $path . $file["name"];
             if( move_uploaded_file($temp_file, $saved_file ) ) {
               return substr( $saved_file, strlen($upload_path)+1 );
             } else {
                 throw new Exception("Unable to move uploaded file $temp_file to $saved_file");
             }
         }
         return false;
    }
    
    static public function UploadErrorMessage($error_code) {
        switch ($error_code) { 
            case UPLOAD_ERR_INI_SIZE: 
                return 'The uploaded file exceeds the upload_max_filesize directive in php.ini'; 
            case UPLOAD_ERR_FORM_SIZE: 
                return 'The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form'; 
            case UPLOAD_ERR_PARTIAL: 
                return 'The uploaded file was only partially uploaded'; 
            case UPLOAD_ERR_NO_FILE: 
                return 'No file was uploaded'; 
            case UPLOAD_ERR_NO_TMP_DIR: 
                return 'Missing a temporary folder'; 
            case UPLOAD_ERR_CANT_WRITE: 
                return 'Failed to write file to disk'; 
            case UPLOAD_ERR_EXTENSION: 
                return 'File upload stopped by extension'; 
            default: 
                return 'Unknown upload error'; 
        } 
    }
}

Usage:
$saved_file = Bumpslide_Util::ProcessUpload( $_FILES['FileData'], dirname(FILE).'/uploads/' );