// returns false if the enter key is pressed call with onkeydown="return noenter(event);"
function noenter(e) {
    return !enterpressed(e);
}

// returns true if the enter key is pressed call with onkeydown="return !enterpressed(event);"
function enterpressed(e) 
{
    var result = false;
    var keynum = 0;
    if(window.event) { keynum = e.keyCode; } // IE
    else if(e.which) { keynum = e.which; } // Netscape/Firefox/Opera
    if (keynum == 13) { result = true; }
    return result;
}