The Internet Archive (archive.org) hosts many legacy software ISOs under "abandonware" provisions. While Microsoft does not endorse this, for educational or archival purposes, you can find verified copies of there. Warning: Always verify the SHA-1 hash of these files to ensure they haven't been tampered with.
If you mount that ISO in a VM and connect it to a network, expect compromise in under 10 minutes. windows server 2003 iso