How do I send information to a PHP document from a PHP document?

[Jess]

I have a PHP document, display.php, that uses information from an HTML document. In display.php, I create a new form that uses another PHP document called display2.php,
Here's my code that is in display.php:
print "<form name = 'advSearch' method = 'post' action = 'display2.php'>";
print "<select name = 'other'>";
print "<option value = '1'>$other1</option>";
print "<option value = '2'>$other2</option>";
print "</select><input type = 'submit'/>";
But I need display2.php to use information from display.php. Is there a way I can send it this information or retrieve this information in display2.php?

Thanks!
I've tried using $_REQUEST for the information from the original HTML form that display.php pulls from but it didn't work. I was thinking it was because display2.php didn't get called from that HTML form. Not sure.