using System;  
using System.Data;  
using System.IO;  
using System.Runtime.InteropServices;  
using Excel = Microsoft.Office.Interop.Excel; 

public class clsExcelWriter : IDisposable  
{  
    private Excel.Application oExcel;  
    private Excel._Workbook oBook;  
    private Excel._Worksheet oSheet;  

    // Used to store the name of the current file
    public string FileName
    {
        get;
        private set;
    }

    public clsExcelWriter(string filename)
    {
        // Initialize Excel
        oExcel = new Excel.Application();

        if (!File.Exists(filename))
        {
            // Create a new one?
        }
        else
        {
            oBook = (Excel._Workbook)oExcel.Workbooks.Open(filename);
            oSheet = (Excel._Worksheet)oBook.ActiveSheet;
        }

        this.FileName = filename;

        // Supress any alerts
        oExcel.DisplayAlerts = false;
    }


    private string GetExcelColumnName(int columnNumber)
    {
        int dividend = columnNumber;
        string columnName = String.Empty;
        int modulo;

        while (dividend > 0)
        {
            modulo = (dividend - 1) % 26;
            columnName = Convert.ToChar(65 + modulo).ToString() + columnName;
            dividend = (int)((dividend - modulo) / 26);
        }
        return columnName;
    }

    public void Dispose()
    {
        // Lets make sure we release those COM objects!
        if (oExcel != null)
        {
            Marshal.FinalReleaseComObject(oSheet);
            oBook.Close();
            Marshal.FinalReleaseComObject(oBook);
            oExcel.Quit();
            Marshal.FinalReleaseComObject(oExcel);

            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();
            GC.WaitForPendingFinalizers();
        }
    }


    public static DataSet OpenFile(string filename)
    {
        DataSet ds = new DataSet();
        using (clsExcelWriter xl = new clsExcelWriter(filename))
        {
            // Iterate through each worksheet
            foreach (Excel._Worksheet sheet in xl.oBook.Worksheets)
            {
                // Create a new table using the sheets name
                DataTable dt = new DataTable(sheet.Name);

                // Get the first row (where the headers should be located)
                object[,] xlValues = (object[,])sheet.get_Range("A1", xl.GetExcelColumnName(sheet.UsedRange.Columns.Count) + 1).Value;

                // Iterate through the values to add new DataColumns to the DataTable
                for (int i = 0; i < xlValues.GetLength(1); i++)
                {
                    dt.Columns.Add(new DataColumn(xlValues[1, i + 1].ToString()));
                }

                // Now get the rest of the rows
                xlValues = (object[,])sheet.get_Range("A2", xl.GetExcelColumnName(sheet.UsedRange.Columns.Count) + sheet.UsedRange.Rows.Count).Value;

                for (int row = 0; row < xlValues.GetLength(0); row++)
                {
                    DataRow dr = dt.NewRow();

                    for (int col = 0; col < xlValues.GetLength(1); col++)
                    {
                        // xlValues array starts from 1, NOT 0 (just to confuse yee)
                        dr[dt.Columns[col].ColumnName] = xlValues[row + 1, col + 1];
                    }
                    dt.Rows.Add(dr);
                }
                ds.Tables.Add(dt);
            }
        }
        // Your DataSet should now be filled! :)
        return ds;
    }
}

}

using System.Data;  
using ExcelWriter;

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            DataSet ds = clsExcelWriter.OpenFile(@"C:\Results.xls");

            // Do some fancy stuff with the DataSet! xD

            while (true) ;
        }
    }
}