I want to apply an XSLT Stylesheet to an XML Document using C# and write the output to a File.
Here is a tutorial about how to do XSL Transformations in C# on MSDN:
http://support.microsoft.com/kb/307322/en-us/
and here how to write files:
http://support.microsoft.com/kb/816149/en-us
just as a side note: if you want to do validation too here is another tutorial (for DTD, XDR, and XSD (=Schema)):
http://support.microsoft.com/kb/307379/en-us/
i added this just to provide some more information.