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.
Procedure
Install vCenter Single Sign-On in a Migration to vSphere 5.5 from a Windows Server 2003 Host Install or Upgrade the vSphere Web Client vSphere Web Client lets you connect to a vCenter Server system to manage your vSphere deployment through a browser. Migrate vSphere Web Client Data from a Windows Server 2003 Host Migrate vCenter Inventory Service Data from a Windows Server 2003 Host Install Inventory Service in a vCenter Server Migration from a Windows Server 2003 Host Migrate vCenter Server Data from a Windows Server 2003 Host Install vCenter Server in a Migration from a Windows Server 2003 Host