If you dont really need Server 2003, why dont you try XP x64 instead ? The x64 versions of XP and Server 2003 share the same kernel. There is a valid, easy to find VLK key for XP x64 Yes XP x64 is different than XP x86.
that is the nice thing about server 2008 no difference in media. I had to go about making sure the CDs for 2k3 I have are VLK media since I have VLK server 2003 keys, it really sucked trying to find x86 Enterprise R2 VLK