The default is to display into an Internet Explorer window. If you download
the other file (The essentials pack) you should be able to get it open in
it's own application. It's called the XPS Viewer EP.
From what I have gathered, it doesn't really seem that you have downgraded
to XP. the only thing that you may have done is reinstall something that has
come already installed with the operating system.
From the link that you provided:
Installation
Installed on Vista, Windows XP, and Server 2003 through Microsoft
Download center
Detect existing viewer and give user a choice to override or not.
XPS viewer can be made the default XPS document viewing application
using "Open With"
XPS viewer can be replaced as the default XPS document viewing
application using "Open With"
Silent install doesn't override existing viewer if available.
Open
XPS Essentials Pack opens in its own application window
Each document is opened in a new instance of the viewer
Files can be opened in one of the following ways:
Double click on an XPS document launches XPS Essentials Pack
Clicking on an XPS Doc link in browser
From within the browser through File --> Open and Open Button
Can open XPS documents from the following locations:
Local machine
File share
Can open a digitally signed document - inform the user that this
document is digitally signed but the digital signature cannot be viewed in
this viewer
Direct link to file:
http://download.microsoft.com/downl...4dc4-9c66-5826cf7c15f7/XPSEP Vista 32 bit.msu