Come ti dicevo sono alle prime armi.
Ho seguito le tue indicazioni
<?php
$user =& JFactory::getUser();
echo "<input type="hidden" name=\"username\" value=\"$user->username\" />";
?>
<div class="form_item">
<div class="form_element cf_heading">
<h1 class="cf_text">Prenotazione Eventi</h1>
</div>
<div class="cfclear"> </div>
</div>
<div class="form_item">
<div class="form_element cf_dropdown">
<label class="cf_label" style="width: 150px;">Evento</label>
<select class="cf_inputbox validate-selection" id="select_1" size="1" title="" name="evento">
<option value="">Choose Option</option>
<option value="1° maggio">1° maggio</option>
<option value="campo protec">campo protec</option>
<option value="fiera di roma">fiera di roma</option>
</select>
</div>
<div class="cfclear"> </div>
</div>
<div class="form_item">
<div class="form_element cf_checkbox">
<label class="cf_label" style="width: 150px;">Turno</label>
<div class="float_left">
<input value="mattina" title="" class="radio validate-one-required" id="check00" name="check0[]" type="checkbox" />
<label for="check00" class="check_label">mattina</label>
<br />
<input value="pomeriggio" title="" class="radio validate-one-required" id="check01" name="check0[]" type="checkbox" />
<label for="check01" class="check_label">pomeriggio</label>
<br />
<input value="intero turno" title="" class="radio validate-one-required" id="check02" name="check0[]" type="checkbox" />
<label for="check02" class="check_label">intero turno</label>
<br />
</div>
</div>
<div class="cfclear"> </div>
</div>
<div class="form_item">
<div class="form_element cf_captcha">
<label class="cf_label" style="width: 150px;">Verifica</label>
<span>{imageverification}</span>
</div>
<div class="cfclear"> </div>
</div>
<div class="form_item">
<div class="form_element cf_button">
<input value="Submit" name="button_3" type="submit" />
</div>
<div class="cfclear"> </div>
</div>
ma ricevo questa sergnalazione
Parse error: parse error, expecting `','' or `';'' in C:\Web\xampp\htdocs\www.aaa.it\components\com_chronocontact\chronocontact.html.php(180) : eval()'d code on line 5
Altra domanda.
Il campo che conterrà il nome utente nella form devo crearlo ??