Currently I use:
To link XSL to XML.
If my xml was here: www.externald
If you're trying to run the XSLT inside .NET, you can easily use the XslCompiledTransform class in .NET to achieve this.
If you're trying to run this on e.g. the command line, there's a bunch of tools you can use to apply a XSLT file to a given XML file - typically however one that's on your local harddisk.
See e.g. Oleg Tkachenko's web site for info on NXSLT and this other XSLT tools, or see this CodeProject article for a Windows shell extension to apply a XSLT to a given XML file (on your local harddisk).
Hope this helps a bit.
Marc