CentOS - Dec 2005 - how to clean up dependencies packages?

Hi,
Does anyone know how to clean up the system, especially the orphan 
packages. I post this in the forum, but it doesnt seems that nobody 
interested in this question. In the beginning, my system did not have 
any kde package but then i installed kaffeine, thus some other kde 
packages has been installed as dependencies but when i yum remove 
kaffeine, only kaffeine was removed. The other packages were left. In 
my Gentoo, i can clean up all the packages that are not installed 
explicitly but i dont know how to do it in centos. Any suggestion are 
welcome.
THAI
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