I just came across the following on the MSDN Subscriber Downloads site:

Special Access to Longhorn and Whidbey PDC Release Code

Active MSDN Operating Systems, Professional, Enterprise, and Universal subscribers may request a set of software distributed at the Microsoft Professional Developers Conference 2003 (PDC), including the preview versions of the "Longhorn" operating system and SDK, and Visual Studio "Whidbey".

Eligible MSDN Subscribers can request the previews by calling MSDN Customer Service. Certified Partners and Breadth ISV / Empower partners should contact their respective Service Centers for further assistance. Note that the preview package contains DVD media, and a DVD drive is required. Please allow 3-4 weeks for fulfillment.