Postfix + Procmail filter

Hello, I would like to install a procmail filter with a global set of rules 
anti-spam ( sames rules for all users ) but I don't find a good guide on the 
net. Moreover it would be easier for me in french but in english it would be 
possible :)

Can someone help me by saying what have I to do, or by giving me a good url plz 
? 

TY