URL tag in Embedded media player

URL value in embedded media player from a javascript variable.
I know I sound bogus so here's what I want...

<Object etc..
<param name="URL" value="??">
* value in the above tag is equal to 'url' variable defined in the script.
</object etc...

and here's my script which lays in a .js file

function LocateMovie() {
var loc = "video/";
var add = document.form.promo.value;
var con = document.form.speed.value;
var url = loc + add + con + '.wmv'
parseFloat(url);
if (add == '') {
alert("Please Select a sample video to view");
} else if (con == '') {
alert("Please select your connection speed");
} else {
location.href = "player.html";
}
}

Thanx a million