spamassassin and postfix question

[Noah]

Hi there my spamd process is running hot on my box.  I am thinking about 
switching my spam filtering process.  I would like to invoke 
spamassassin on a per incoming email basis. I am using postfix for the 
MTA and also have mailman mail lists.  Is it good to run spamassassin 
for incoming emails to the lists or not and let the mail list admin have 
more control over those things?

clues about how to configure all this to the new invoking process is 
helpful.   I found a few websites via searching but I am wondering if 
somebody knows of a really nice concise site for all this.

Cheers,

Noah