1.onkeydown在ie6中捕捉不到回车事件，用onkeypress代替
2.例子
<input type="password" onkeypress="f(event)"/>
function f(event ){
event = event?event:window.event;
var key = event.keyCode?event.keyCode:event.which;
if(key==13){
}
}
function f(){
var event = arguments[0]||window.event;
var key= event.charCode||event.keyCode;
if(key==13){
}
}