There are several available options for managing emails in Sharepoint Portal Server or Windows Sharepoint Services. I've researched a couple and found some pro's and con's:
Configuring Email enabled Document Libraries
This is the WSS supported way of doing things. Described by MS here. Basically you create a public folder in Exchange that users can send emails to. Then you enable email for document libraries in Sharepoint Administration. Then you set up a doc lib to poll an exchange folder on a given interval. When a new item is found with an attachment, the attachment is added to the document library along with meta data about sender, recipient, subject and date. The message body remains in exchange and is not available in the document library. This approach allows anyone to send an email with an attachment that will appear in the doc lib. A useful, but risky, approach to for instance allow XML documents to be sent in and start up cool stuff via document library event handlers.
Using third party web parts with exchange
CorasWorks recently acquired BizBox Software and their Outlook web parts. You can use their "My Workplace for Outlook" to get a full Outlook experience on your teamsite. Useful, but in many scenarios you simply want to store a set of emails related to whatever purpose your teamsite has.
Saving emails from outlook to a standard document library
By using the standard File -> Save As option in outlook and saving a message in the outlook *.msg format users save emails as they would with word documents. In order to make the message header and body searchable by sharepoint a third-party IFilter needs to be installed. When users click emails in the document library they open directly in outlook including attachments. There have been some blogging about problems with large attachments (over 3mb) not being stored properly, but I have done no further research at the moment. Setting an outlook template file as the document template for such a library and clicking New Document returns this popup:
'New Document' requires a Windows SharePoint Services-compatible application and Microsoft Internet Explorer 5.0 or greater. To add a document to this document library, click the 'Upload Document' button.
But I would presume that this can be hacked with some effort in Sharepoint to open Outlook. The last thing to note is that the properties of a msg file is not mapped like properties of a Word document. That is, you cannot create columns called "To", "From" and "Subject" and expect the values to be mapped automatically. You can, however, create a document library event handler for this, but that would require either knowledge of the msg format, or using the unmanaged outlook api's (pure guessing actually).
When using this approach we just got confronted with another, yet unresolved problem. The users need to be able to have the email doclibs as favorites in outlook. Sharepoint eventlists (calendars) appear under a mysterious "Sharepoint folders" in Outlook; the quest goes on to see if this is possible.
Also check out Jim's post (and frustration) related to this.