vCenter Server 5.5 does not support Windows Server 2003 as a host machine, and does not support upgrades from Windows Server 2003 hosts. You can install vCenter Server 5.5 and related components on a supported host and migrate configuration data from your existing Windows Server 2003 installation.
Before you begin
Verify that the new host machine meets the requirements for vCenter Server 5.5. See System Requirements.
Review the topics in Preparing for the Upgrade to vCenter Server.
Download the vCenter Server installer.