No es complicado, te doy una idea:
Código PHP:
<?php
if(isset($_REQUEST['submit']))
{
/* Realiza el UPDATE */
mysql_query("UPDATE tabla SET campo1='".$_REQUEST['campo1']."' WHERE id_campo='".$_REQUEST['id_campo']."' LIMIT 1");
}
/* Realiza la consulta */
$campos = mysql_fetch_array(mysql_query("SELECT * FROM tabla WHERE id_campo='".$_REQUEST['id_campo']."' LIMIT 1"));
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>Algo</title>
</head>
<body>
<form action="prueba.php" method="post">
<input type="text" name="campo1" value="<?=$campos['campo1']; ?>" />
<input type="hidden" name="id_campo" value="<?=$_REQUEST['id_campo']; ?>" />
<input type="submit" name="submit" />
</form>
</body>
</html>