SpamPal sits between your email program and your mailbox, checking your email as you retrieve it. Any email messages that it considers to be spam will be "tagged" with a special header; you simply configure your email client to filter anything with this header into a separate folder and your spam wont be mixed up with the rest of your email anymore.
Unlike other anti-spam programs, Windows XP/2000 users require no setup changes to their email username/servers!