search your drive for something you have downloaded using BitTorrent

You almost never can preview BitTorrent files. It doesn't work the same way as Limewire (meaning it downloads pieces from the whole file not in consecutive order but random) It just takes whats available at that instant.

Also a lot of the files are packed with e.g. WinRAR

LimeWire isn't supposed to download contiguous chunks either. It's probably just more likely. I've also read that the original BitTorrent client shuffles chunks around as long as the file is incomplete. That's probably just a side-effect caused by the method it uses to allocates disk space.