Uploads go to the defined temp-dir (check your php.ini for "upload_tmp_dir = "), or if not defined the system's default temp-dir. After checking whether the upload was OK, you can move the file anywhere with:
if( is_uploaded_file( $sFile ) )
{
$bFileResult = @move_uploaded_file( $sFile, $sDirectory . "/" . $sFile_name );
}
with $sDirectory where you want to move the file. Beware: $sFile contains the temporary file name assigned by PHP, $sFile_name is the original file name, $sFile_size is the size. More info to be found on http://www.php.net/manual/en/features.file-upload.php
Even easier is to change the default tmp-file to the directory you want, just make sure it's writable for your webserver (possible security hazard!).