passing values to javascript functions

How can I pass a value from a php page to a javascript function that calls a pop up window of another php page? Please keep reply in child like terms, thanks.

Here's an example:

<SCRIPT type="text/javascript">
function rand() {
// shows a random image (randomized at the server)
document.location = "<?php echo "$PHP_SELF?i=$rand" ?>"
}
</SCRIPT>

The document containing this is a .php file, if that's not obvious. This way, you can assign variables, or generate function calls or whatever using variables accessible to your PHP script. Just echo the PHP variables where you want them in your Javascript.

You might want to give us a bit more information if you want a specific answer - is it to the same page or different pages, etc.? It can be done but there are many different combinations and permutations (e.g. I've got some script which sends a value to a search page located in a frame in the pop-up window - the value coming from a drop down menu).

Emps