Passing Variables derived from objects

[Force]

I want to assign the value of an object on the current form to a variable and then pass that variable in the url to the new page.
I'm not having any luck with this. I think that I'm all around it, but I can't make it click. Can someone point me in the right direction? Thanks for the help.

Mark F.

<script language="JavaScript">
function preview(){
var fname = document.myform.fname.value;
window.open('preview.cfm?fname='+fname','mywindow','width=800,height=600,scrollbars=yes');
}

[Fang]

function preview(){
var fname = document.myform.fname.value;
var url="preview.cfm?fname="+fname;
window.open(url,'mywindow','width=800,height=600,scrollbars=yes');
}