Calling Input Button Click Manually

In my javascript, when enter key is pressed, I want to simulate the effect
of clicking a button.

var mykey;
var posted=false;

if (window.Event){
document.captureEvents(Event.KEYDOWN);
}

document.onkeydown = myKeyDown;

function myKeyDown(e){

if (window.Event){
mykey = e.which;
}
else{
mykey = event.keyCode;
}
//alert(mykey);

var theform;
if (window.navigator.appName.toLowerCase().indexOf("netscape") > -1) {
theform = document.forms["Form1"];
}
else {
theform = document.Form1;
}

if ((mykey==13) && (posted==false) && (theform.btnSend.click))
{
posted=true;
theform.btnSend.click();
}
}

Everything works fine in IE4 to IE6. But NS behaviour is really bizzare.

Thing work as expected in NS7.

In NS6, theform.btnSend.click() does not cause form submission.

In NS4, it complains that theform.btnSend.click() does not exist (despite
having passed the if test that verifies theform.btnSend.click exists).