Relative paths in an ASP.NET application code behind

Server.MapPath - returns the path of the relative path; ~ ensures the relative path is related to the application root

xDoc.Load(Server.MapPath("~/Templates/template.cfg"));

I would probably use

xDoc.Load(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Templates", "Template.cfg"));

This makes your XML loading code independent of ASP.NET. If you were to reuse it in, say, a Windows Forms application, this would give a path relative to the directory containing the Windows Forms exectuable.

xDoc.Load("~/Templates/template.cfg");

might work?