LinuxQuestions.org - Email and shared contacts/calandar, etc

I've searched around a fair bit for the best way of approaching this problem, but I still remain somewhat confused - Can you help?

I have a small home network that consists of a Slackware Linux machine basically acting as a file server using Samba. This is serves a couple of XP machines and a laptop that is hug off a wireless lan. All of this is connected up through a simple 8 port switch.

Sadly I cannot connect to ADSL, so I connect top an ISP through an ISDN, Home Highway connection.

What I would like to do is:
- have my linux box collect and forward email
- be able to access individual mailboxes from any of the machines
- be able to share a common contacts and perhaps calendar.

I'm confused as to whether I should use LDAP for the contacts and then an IMAP server for the mail and contacts, or whether I could use IMAP for all of it? I have come across the "Postfix or POP Toaster", would this be a good approach.

Any help would be welcome that would point me to the right approach. I could then focus my research on installing the software.

Many thanks