Well Vista should have MSXML 3 and MSXML 6 , both supporting XSLT and XPath 1.0. So there is no need to install anything. If you want to use with with PHP then I think you can do e.g.
Code:
$doc = new COM("Msxml2.DOMDocument.6.0");
but I have never done that.
PHP 5 also comes with libxslt as its XSLT 1.0 processor, not sure whether that is installed by default or you need to enable it as an extension. See
http://www.php.net/manual/en/xsl.installation.php for details.
Vista also has .NET 3.0 as far as I know, so you can run .NET application using System.Xml.Xsl.XslCompiledTransform which also support XSLT 1.0. I am not sure you could use that with PHP however.
If you want to use XSLT 2.0 then on Windows you can install Saxon 9 or AltovaXML tools, I am not sure which is better accessable from PHP.