Good afternoon Ms Wallace,

The 64-bit version of Windows Server 2003 is not officially supported at the moment.

Although no actual issues were reported about it, there COULD potentially be issues because of this. Even though it would work, it would be safer to install on a fully supported OS version.

Please refer to this link for all hardware and software requirements.
Planet Press 7 release notes (check the "note 1" at the bottom)

Feel free to follow up if you have any more inquiries, it will be my pleasure to help you clarify them.

Have a nice afternoon,