Window.Open Function Problems

I'm redesigning my webpage and thought it would be a good idea to have windows popup if someone had a question about terminology. So basically, I wrote a small function that was supposed to popup a 400x300 window centered towards the top left of the screen with some basic parameters...
this code is inserted into the head

Code:

<Script Language="JavaScript 1.1" type="text/javascript;version=1.1">
function jargon(url){
var screenw = 800;
var screenh = 600;
screenw = screen.width;
screenh = screen.height;
var mywin = window.open(url, 'jargon', 'left=screenw / 4, top=screenh / 4, width=400, height=300, toolbar=0, menubar=0, resizeable=0, status=0');
}
</script>
(the screenw and screenh are meant for older browsers)
which is meant to be embedded in the code like....

Code:

<a href="#" onclick="jargon('../jargon/php.php');">PHP</a>
But whenever I try this, it just uses the # link and nothing happens.