I'd like to add some more information on the Ximian Evolution on Mac OS X idea. If you are connecting to a Microsoft Exchange™ server you will only be able to talk POP or IMAP to the server. There is Ximian Connector™ for Microsoft Exchange™, which will let you utilize the most useful features of Exchange (office calendaring, resource scheduling, etc...). Alas it is only for the supported (read: linux) distributions. Ximian supports Yellow Dog, but I can't find any information about PPC support for Connector.
So, for those of you tied to Outlook, you should first find out if Outlook is tied to Exchange. If it is, Evolution on Mac OS X isn't the solution for you. In fact, I don't think Evolution on Mac OS X is the solution to anything right now as there are a number of very capable e-mail clients available. But if you need to talk to Exchange you will need to wait until Microsoft Entourage supports Exchange. Of course, the rumors are that only Exchange 2000 will be supported and not 5.5. Personally I doubt that. True it would be a very Microsoft thing to do, ensuring more people going down the upgrade path. But in reality the number of mac users in an organization probably wouldn't be able to squeak enough to get the grease that would be an upgrade to Exchange 2000. Plus, Outlook 2001 for Mac already talks to Exchange 5.5.
It's all just speculation and rumors at this point though, especially since Exchange 2003 is getting ready to be rolled out. Boy, I can't really express how happy I am not to be an Exchange admin right now. Discuss