How to keep a changed variable value inside a specific div?

[waynelark]

\[code\]<?php $_SESSION["msgReg"]="333";?><form id="formReg" action="reg.php" method="post"> // reg.php is another file<div id="regInfo"><?php echo("{$_SESSION['msgReg']}"); ?></div>...\[/code\]Inside \[code\]reg.php\[/code\] variable \[code\]msgReg\[/code\] is changed to \[code\]444\[/code\] or whatever, but in \[code\]regInfo\[/code\] (starting page) is still - \[code\]333\[/code\]
How can I write the new value inside already existing div - \[code\]regInfo\[/code\] ?