Rorschach

Get it from here, there's a windows installer: http://bitconjurer.org/BitTorrent/

On linux anyway you have to install it, then configure your browser to use the bittorrent client to open files with a .torrent extention (dunno how you'd do that on windows but it won't be difficult). Then you browse sites like http://www.suprnova.org/ looking for .torrent files, click on them and download. There's no actual client that you use to search for files like Kazaa, it's all done through your browser.