Late in 2007 the XML Paper Specification (XPS) was published. The means to create, view and print XPS files are integrated in you Windows OS, dare I say it is as ubiquitous as PDF and you may not even know it. If you don’t have the XPS features installed you can get it free from Microsoft or one of the many 3rd party vendors deploying solutions for XPS.
XPS Showcase
What is an XPS document?
The XML Paper Specification itself is platform independent, openly published, and available royalty-free and Microsoft has integrated XPS-based technologies into Microsoft Windows Vista operating system and the 2007 Microsoft Office system. Microsoft brings additional document value to its customers, partners, and the computing industry through the XPS-based technologies.
An XPS document is any file that is saved to the XML Paper Specification, or .xps, file format. You can create XPS documents (.xps files) by using any program that you can print from in Windows; however, you can view XPS documents only by using the XPS Viewer, which is included in this version of Windows.
An XML Paper Specification (XPS) document is a document format you can use to view, save, share, digitally sign, and protect your document’s content. An XPS document is like to an electronic sheet of paper: You can’t change the content on a piece of paper after you print it, and you can’t edit the contents of an XPS document after you save it in the XPS format. In this version of Windows, you can create an XPS document in any program you can print from, but you can only view, sign, and set permissions for XPS documents in the XPS Viewer.
XPS FTS in MOSS 2007
The XPS format is great for SharePoint. Not only for view-ability but for it’s Full Text Search-ability (FTS). The following is a step-by-step guide to enabling and configuring XPS IFilter support in Windows Server 2008 and MOSS 2007. Note: I have a single server running all my MOSS farm services. If I had a distributed farm with my MOSS Index service running on a dedicated server I would enable and configure the XPS feature on the dedicated Index server.
Step-By-Step
1. On the MOSS Index server launch the Server Manager and select Add Features, select the XPS Viewer and click Next.

2. Click Install.
3. Click Close.
4. From the SharePoint 3.0 Central Administration select the Share Service Provider/Search Settings and under Crawling select File types and then select New File Type.
5. Enter xps and click on OK.
6. You will see the new file type in the list.
7. You can also confirm it has been enabled by reviewing the registry setting for the following key.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\12.0 \Search\Applications\<SITE-GUID>\Gather\Portal_Content\Extensions\ExtensionList
8. Next you’ll need to enter the following details in the HKLM hive for the XPS ifilter.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\12.0\Search\Setup\Filters\ .xps]
Default = (value not set)
Extension = xps
FileTypeBucket REG_DWORD = 0×00000001 (1)
MimeTypes = application/xps
9. In addition, you’ll need to add and set the Class ID for the XPS iFilter in the following HKLM hive location.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\12.0\Search\Setup\ContentIndexCommon\Filters\Extension\.xps]
Set the "Default" value to the CLSID of XPS IFilter.
Default REG _SZ = {1E4CEC13-76BD-4ce2-8372-711CB6F10FD1}
10. Next, stop and start the Office SharePoint Server Search service.
C:\>net stop osearch
C:\>net start osearch
11. Next, run a full or incremental crawl. If you’re interested, keep an eye on the C:\Users\<search-service-account>\AppData\Local\Temp\gthrsvc folder and you’ll see MOSS crawl writing the images to this folder to index. This of course is why you need a beefy server for Indexing, lot’s of file IO.

12. Once the crawl is complete you can verify the XPS files have been crawled via the Crawl Log’s URL Summary.
Searching
When I search for the keyword “galleries” in MOSS Advanced Search I get hits from the result FTS.
For More Information
XML Paper Specification: Overview
ECMA International XPS Specification and Reference Guide
ECMA International XPS White Paper
Microsoft MSDN XPS Team BLOG