export datagridview to xls file

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VB

I have this function that export a datagridView in Excel sheet :

public void ExportGridToExcel(DataGridView TheGrid, string FileName)
    {

            using (System.IO.StreamWriter fs = new System.IO.StreamWriter(FileName, false))
            {
                fs.WriteLine("<?xml version=\"1.0\"?>");
                fs.WriteLine("<?mso-application progid=\"Excel.Sheet\"?>");
                fs.WriteLine("<ss:Workbook xmlns:ss=\"urn:schemas-microsoft-com:office:spreadsheet\">");
                fs.WriteLine("    <ss:Styles>");
                fs.WriteLine("        <ss:Style ss:ID=\"1\">");
                fs.WriteLine("           <ss:Font ss:Bold=\"1\"/>");
                fs.WriteLine("        </ss:Style>");
                fs.WriteLine("    </ss:Styles>");
                fs.WriteLine("    <ss:Worksheet ss:Name=\"Sheet1\">");
                fs.WriteLine("        <ss:Table>");
                for (int x = 0; x <= TheGrid.Columns.Count - 1; x++)
                {
                    fs.WriteLine("            <ss:Column ss:Width=\"{0}\"/>", TheGrid.Columns[x].Width);
                }
                fs.WriteLine("            <ss:Row ss:StyleID=\"1\">");
                for (int i = 0; i <= TheGrid.Columns.Count - 1; i++)
                {
                    fs.WriteLine("                <ss:Cell>");
                    fs.WriteLine(string.Format("                   <ss:Data ss:Type=\"String\">{0}</ss:Data>", TheGrid.Columns[i].HeaderText));
                    fs.WriteLine("                </ss:Cell>");
                }
                fs.WriteLine("            </ss:Row>");
                for (int intRow = 0; intRow <= TheGrid.RowCount - 2; intRow++)
                {
                    fs.WriteLine(string.Format("            <ss:Row ss:Height =\"{0}\">", TheGrid.Rows[intRow].Height));
                    for (int intCol = 0; intCol <= TheGrid.Columns.Count - 1; intCol++)
                    {
                        fs.WriteLine("                <ss:Cell>");
                        fs.WriteLine(string.Format("                   <ss:Data ss:Type=\"String\">{0}</ss:Data>", (TheGrid.Rows[intRow].Cells[intCol].Value != null) ? TheGrid.Rows[intRow].Cells[intCol].Value.ToString() : string.Empty));
                        fs.WriteLine("                </ss:Cell>");
                    }
                    fs.WriteLine("            </ss:Row>");
                }
                fs.WriteLine("        </ss:Table>");
                fs.WriteLine("    </ss:Worksheet>");
                fs.WriteLine("</ss:Workbook>");
            }
}

If i try to open the generated XLS with Microsoft Excel everything is ok, but if try to open with OpenOffice Calc, give me an import screen and i can't open the spredsheet.

Why ? How can i do for export an Excel sheet compatibile with openoffice calc ?
I want to exceute the xls file in both either ms office or open office it should work.with out adding com component. I am using .net framework 2.0 and server 2005can any help