Excel.Application excel_app;
excel_app = new Excel.Application();

#if MSO2000
	Excel.Worksheet excel_worksheet = (Excel.Worksheet) excel_app.Workbooks.Open(TemplatePath + "Blank_Table_1.7.xls", Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing ).Worksheets.get_Item( 1 );
#else
	Excel.Worksheet excel_worksheet = (Excel.Worksheet) excel_app.Workbooks.Open(TemplatePath + "Blank_Table_1.7.xls", Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing).Worksheets.get_Item( 1 );
#endif

excel_range = excel_worksheet.get_Range("A1", Type.Missing);

... добавляем листы к книге ...
... заполняем поля ....

excel_range = null;
excel_worksheet = null;
excel_app = null;
GC.Collect();
GC.GetTotalMemory(true);