HTML - forms best practice
===

It's OK to have a form with more  submit buttons?
I mean I have a form which contains some input fields and a table and 
3 buttons which will export some information in different formats

    <form id="form1" name="form1" method="post" >
        <label for="country"><strong>Countries: </strong></label><br />
        <select id="country" name="country">
          <?php
          //some php code here
          ?>
        </select> 
        <br />
        <br/>
        <label for="start_date"><strong>Start date: </strong></label><br />
        <input name="start_date" type="text" id="start_date" value="<?php if(!empty($start))echo $start; ?>" size="20" />
        <br />
        <br />  
        <label for="stop_date"><strong>Stop date: </strong></label><br />
        <input name="stop_date" type="text" id="stop_date" value="<?php if(!empty($stop)) echo $stop; ?>" size="20" />
        <br />
        <br />
            <input type="submit" name="fill_table" value="Retrieve data" /> 
        
        <div id="table">
          <h1>&nbsp;</h1>
          <hr />
          <h2>Sales Report</h2>
            <table class="display" id="data_table" >
              <thead>
                  <tr>
                    <th>Product</th>
                    <th>Date</th>
                    <th>Quantity</th>
                  </tr>
              </thead>
              <tbody>
                <?php
                    //some php code here
                ?>
              </tbody>
            </table>
            <br />
            <br />
            <br />
            <input type="submit" class="button" name="export_xls" value="Export xls" />
            <input style="margin-left:10px;" type="submit" name="export_html" value="Export html" />
      </form>

Is it ok to do it this way or should i make 3 forms each one having a particular submit button? Each time i press a submit button I'm intrested in the input fields :start_date, stop_date and the selected item from "country".
P.S. I want to know if it's optimal and how other programmers would handle this stuff