WINDOW.OPEN using POST instead of GET

function toPreview(f) {

f.action = "";

f.onsubmit = "return true;";
f.target ="preview";

var theHeight = 550;
var theWidth = 480;
var theTop=(screen.height/2)-(theHeight/2);
var theLeft=(screen.width/2)-(theWidth/2);
var features='height='+theHeight+',width='+theWidth+',top='+theTop+',left='+theLeft+",scrollbars=yes";
window.open('','preview',features);
}