try the following :
References and namespaces:
using Microsoft.Office.Interop.Excel;
using Microsoft.Office.Interop.InfoPath.Xml;
using System.Xml.Xsl;
using System.Xml;
XmlDataDocument xmlDoc = new System.Xml.XmlDataDocument(CVDtls);
XslCompiledTransform xslTran = new System.Xml.Xsl.XslCompiledTransform();
FileStream fs = new System.IO.FileStream(@"C:\EXPORTED\test.xls", FileMode.OpenOrCreate);
XmlTextWriter xtw = new System.Xml.XmlTextWriter(fs, System.Text.Encoding.Unicode);
xtw.WriteProcessingInstruction("xml", "version='1.0'");
string strXSLFilename;
strXSLFilename = "test.xsl";
xtw.WriteProcessingInstruction("xml-stylesheet", "type='text/xls' href='" + strXSLFilename + "'");
CVDtls.WriteXml(xtw);
xtw.Close();