[CentOS] clarifications

Hello all,

    I've been trying to get spamassassin and clamav working, but got 
really confused when I realized there are various incarnations of the 
software.  Originally, I started out with just spamassassin, but learned 
there is also an SA-milter.  Can someone tell me which of the various 
spam fighting packages i.e., sa, sa-milter, clamav, clamave-milter, and 
so forth?  I ran into problems with one package with the system not 
being able to open a socket, so I just gave up.  I hope I'm not too 
vague here, but essentially, I just would like to know what the milter 
part does, and if that's the way to go, or the non-milter versions. 

    I'm subscribed via digest, and if it's not too much trouble, I'd 
appreciate a cc direct to me.  Many thanks..

Sam