Cross-platform mail/file/calendar server

I've got a client who currently has an investment in some PCs. He wants to add a couple of systems, and he's thinking about going Mac. There's a couple of different options and I'm hoping to steer him towards replacing his current systems with Macs and getting a Mac server. He wants to have his own email server, share calendar information, and share files. So what I need to know is this: 1) If he decides to stick with PC client computers but get a Mac server, I know it can handle file sharing and email, but does it handle Calendar sharing with Outlook or some other PC software? 2) If he decides to replace the PCs with Macs, but he wants to get some more value out of one of he PCs and use it as a server, other than going Exchange server or Linux, is there a simple way to set up an email/calendar server? Thanks in advance for any information. Jeff Langston jeff_langston mac.com