You can sign up now to receive trial software for Windows Server 2003, Enterprise Edition, for 64-Bit Extended Systems via CD or download. Read about the Customer Preview Program (CPP) and the different options for obtaining the pre-release software, and then use the links on the right to register to order the CD Kit or download product files. Note that in either case, the pre-release software is time limited and will expire in 360 days. Sign up over here
Thanks to ChrisCustom in our forums for the information.