After a small search on the web, I came to a CentOS page 
(http://www.centos.org/modules/smartfaq/faq.php?faqid=24) which mentions:


"If you need to install bittorrent for CentOS, rpms are available from Dag's repository:

http://dag.wieers.com/packages/bittorrent/
(Latest el3 version for CentOS-3 and el4 version for CentOS-4)"


In Dag's repository there is the latest version of BitTorrent for Red Hat EL4 as 
bittorrent-gui-4.4.0-1.2.el4.test.noarch.rpm with a date of 1 February 2006. I wonder why 
it is still in "test" after a whole of 4 months...