The Ximian Connector for Microsoft Exchange allows Ximian Evolution clients to access accounts on Microsoft Exchange 2000 servers. It is available through Ximian Red Carpet in its own channel or through novell's website. See the product's site for more details: https://store.ximian.com/xproddetail.php?sku=XCN14-DL-U01.
Unlike the regular Ximian Evolution client, the Ximian Connector for Microsoft Exchange is proprietary software and source code is not available.
Edit by jbreland:
Thanks, Andrew! Actually, the connector has, in fact, recently been GPL'ed. This happened a few months ago, thanks to Novell. Details about this can be found in the Evolution 2.0 press release from Novell.