the uTorrent client was recently updated (or "µTorrent", as it's really called).
uTorrent is like many other BitTorrent clients, except for a few notable things. while trying to copy the features and look of Azureus (the most popular BitTorrent client) its is able to use significantly less resources.
while Azureus requires that the Java runtime environment and itself both be installed, uTorrent is a native Windows application, and doesn't require anything else installed. as of version 1.2, uTorrent is just 105K total in size. typical ram usage is around 6 megs or less. Azureus would sometimes take up 64-80 megs of ram, even when on no torrents!
you can get uTorrent here: http://www.utorrent.com/