About XPS file - I have updated the following blog posting with additional details on XPS file
Indexing XPS documents with MOSS 2007
XPS Viewer, printer drivers, IFilter
Microsoft XPS Document Writer - a printer driver that allows you to do "Print to file" to save webpage as a XPS file
Microsoft Office 2007 Add-in: Microsoft Save as PDF or XPS
Feel free to add to my comments with any useful XPS and/or SharePoint related links and I will include them here.