yes UDMA 100 or 133 HDs are backward compatible with UDMA 33 or 66 mobo

k-lite and kpp are hard to find nowadays. google too it seems removed links to the download sites. e-mule is too slow but still most of the times the stuff in progress will get finished ultimately. kpp(kazaa) is better and faster sometimes than e-mule/donkey you might also want to try, http://www.suprnova.org which needs a small client for those bit torrent files, might as well find kpp over there in the list of torrents.