function checkEnter(e) { //e is event object passed from function invocation
    var characterCode;

    if (e && e.which) { //if which property of event object is supported (NN4)
        e = e;
        characterCode = e.which; //character code is contained in NN4's which property
    }
    else {
        e = event;
        characterCode = e.keyCode; //character code is contained in IE's keyCode property
    }

    if (characterCode == 13) { //if generated character code is equal to ascii 13 (if enter key)
        document.forms[0].submit();  //submit the form        
        return false;
    }
    else {
        return true;
    }
}