header("Location" http://site.com/component/option,com_estateagent/Itemid,99999999/act,object/task,showEO/id,".$_POST."/");
<form name="form1" method="post" action="">
<form name="form1" method="post" action="./action.php">
header("Location: http://site.com/component/option,com_estateagent/Itemid,99999999/act,object/task,showEO/id,".$_POST."/");
<?php header("Location: http://site.com/component/option,com_estateagent/Itemid,99999999/act,object/task,showEO/id,".$_POST."/"); ?>
<form name="form1" method="post" action="./action.php"> <label> <input name="textfield" type="text" size="5"> </label> <label> <input type="submit" name="Submit" value="Перейти"> </label> </form>