The XPS v1.0 specification has been released and can be found at http://www.microsoft.com/whdc/xps/downloads.mspx.  The final release of Windows Vista is compatible with v1.0.  

After a quick toast of champagne and hand shaking, the final printed spec was signed by the team and sent to Microsoft Archives for safekeeping.  The XPS team would like to thank the industry for their ongoing feedback throughout the development of the specification.  We look forward to seeing the creative and compelling ways that you integrate XPS into your products.