I have introduce many XPS tools before, and today I find another great XPS viewer, java-axp.
java-axp is a 100% java XPS file reader. The goal of the project is to create a java library for parsing, reading and rendering XPS documents in java.

The project currently consists of two core OSGi bundles, xps-core and xps-swingviewer. The xps-core bundle provides a document model and a file input layer. The xps-swingviewer bundle provides several Swing components to render XPS documents.
for details, please visit http://code.google.com/p/java-axp/

Software Imaging have released a new XPS viewer as a free download. The viewer uses Software Imaging’s own PrintMagicXPS technology to render the XPS documents, which differs from other XPS viewers because it is developed in C++ native code, and therefore has no dependency on .Net or managed code.

Features include:

• High quality rasterizer which leverages Software Imaging’s PrintMagicXPS technology
• Full compliance with the XPS 1.0 specification
• Easy to use and view your XPS documents
• Priority given to the rendering of the first page of a multiple page XPS document
• Multi-threaded application for improved performance on multi-core systems
• Developed in C++ native code, therefore no dependency on .Net and managed code
• Two rendering modes: Aliased and Anti-Aliased
• Zoom and rotate views
• Colour management

Supported Operating Systems

• Microsoft Windows Vista
• Microsoft Windows Server 2003
• Microsoft Windows XP SP2

Prerequisites on Download Page

To run XPS Viewer on Windows XP Service Pack 2 or Window Server 2003 the following components will need to be downloaded and installed:

• Microsoft Core XML Services (MSXML) 6.0
• Microsoft Windows Imaging Component (WIC)

btw, Windows 7 Will Include New Win32 API’s For XPS, and the new API’s will be:

• XPS API provides creation, manipulation, reading, writing and other services for XPS documents and print streams
• OPC API provides creation, manipulation, reading, writing and other services for Open Packaging Conventions-based file formats, including XPS, OOXML and an increasing number of industrial strength third party file formats
• XPS Print API provides a new entry point for applications to benefit from the enhanced XPS Print Path, irrespective of whether the final output device supports XPS

reference,
http://digitaldocuments.debenu.com/2008/11/12/windows-7-will-include-new-win32-apis-for-xps/
http://digitaldocuments.debenu.com/2008/10/01/new-xps-viewer-from-software-imaging/
http://softwareimaging.com/products-services/XPSViewer/index.asp

After installed either .Net Framework 3.0 or the XPS Essential Pack on Windows XP SP2/Windows 2003, or you use Vista, you would discover that a “Microsoft XPS Document Writer” appeared in your “Printers and Faxes”. but what is it?
The Microsoft XPS Document Writer (MXDW) is a print-to-file driver that enables any Windows XP SP2/2003/Vista application to create XML Paper Specification (XPS) Document files.

An XPS file is in fact a ZIP archive using the Open Packaging Convention, which contains the files which make up the document. These include an XML markup file for each page, text, embedded fonts, raster images, 2D vector graphics, as well as the digital rights management information. The contents of an XPS file can be examined simply by opening it in an application which supports ZIP files.

As you know, it is not a easy job to convert PDF to XML, even using Adobe Acrobat, but I found The Microsoft XPS Document Writer can easily print PDF to XML, also including images.
But it has an issue when you try to Print the PDF document double-byte characters(for example Chinese PDF document), all double-byte characters will be converted to vector graphics.