Do you mean you want to use the Linux PDC as the email server? If so you probably already have pop3 installed. Create a user account for each user you want to get mail (I assume this is already done since it is a PDC) and make sure pop 3 is turned on in inetd/xinetd.
Configure sendmail to recieve SMTP mail. If you are behind a firewall you will have to forward the SMTP port to this server.
Create an MX record in your DNS domain to point to your server (firewall address if using port forwarding).
Point your Windows (ick) clients to your PDC for pop3 (imap is better, keeps mail folders on server sort of like Exchange).
[ November 20, 2002: Message edited by: void main ]