Rules for filtering spam that comes written in russian alphabet, Mail 4.5, OS 10.6.8
From MacHints:


Select Mail -> Preferences -> Rules
Select Junk -> Edit
Select (+) to add a new rule.
Click on the "From" drop-down and select "Edit Header List..."
Add "Content-Class" by typing "Content-Class" in the "Header:" text box and then hit "Add Header" and "OK."
Set the first pop-up on your new rule to Content-Class, the second to Contains, and the third to charset="windows-1251".
Select (+) to add a new rule.
Set the pop-ups to Subject, Contains, and charset="windows-1251".
Select (+) to add a new rule.
Set the pop-ups to From, Contains, and charset="windows-1251".
Click the "OK" button to end the rule definition.