In the SilkPerformer Release Notes Tested Software section we see an extensive list of supported Operating Systems.  Later in the Release Notes, under the Citrix support section we see the following smaller list of supported Operating Systems:

Operating Systems:

• Microsoft Windows XP
• Microsoft Windows Server 2003
• Microsoft Windows Server 2008

This particular list refers to the tested and supported Citrix server Operating Systems whereas the previous list refers to the Operating System which SilkPerformer itself has been tested on.