Send a variable to one of those scripts, then load that script, then use a hidden input to send that variable to the other script.
//formpage.html
<html>
<head><title>Big Fat Blahs!</title></head>
<body>
<form name="foo" action="form1.php" method="post">
<input name="bar" type="text" value="blah" />
<input name="submit" type="submit" value="Submit" />
</form>
</body>
</html>
//form1.php
<html>
<?php
if(!isset($_POST['submit'])) {
header("Location:formpage.html");
} else {
?>
<head>
. . .
<form name="qux" action="form2.php" method="post">
<?php
echo "<input name=\"quxu\" type=\"text\" value=\"".$_POST['bar']."\" />";
}
?>
<input name="submit2" type="submit" value="Submit" />
</form>
</body>
</html>
//form2.php
<html>
<?php
if(!isset($_POST['submit2'])) {
header("Location:formpage.html");
} else {
?>
<head>
. . .
<?php
echo "This the value that has been passed: ".$_POST['quxu'];
//outputs blah
}
?>
</body>
</html>
Hope this gives you an idea!
