有条件的话设置position:absolute 然后改z-index<iframe src="http://www.baidu.com" style="position:absolute;" id=i1></iframe>
<iframe src="http://www.google.com" style="position:absolute;" id=i2></iframe>
<BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR>
<INPUT TYPE="button" onclick="g()" value="shwo baidu">
<INPUT TYPE="button" onclick="b()" value="show google">
<SCRIPT LANGUAGE="JavaScript">
function g()
{
document.getElementById("i1").style.zIndex = 99
document.getElementById("i2").style.zIndex = 95
}
function b()
{
document.getElementById("i1").style.zIndex = 95
document.getElementById("i2").style.zIndex = 99
}
</SCRIPT>
<iframe src="http://www.google.com" style="position:absolute;" id=i2></iframe>
<BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR><BR>
<INPUT TYPE="button" onclick="g()" value="shwo baidu">
<INPUT TYPE="button" onclick="b()" value="show google">
<SCRIPT LANGUAGE="JavaScript">
function g()
{
document.getElementById("i1").style.zIndex = 99
document.getElementById("i2").style.zIndex = 95
}
function b()
{
document.getElementById("i1").style.zIndex = 95
document.getElementById("i2").style.zIndex = 99
}
</SCRIPT>
<body bgcolor='black'>
<script type='text/javascript'>function doChange() {
var s1 = document.getElementById("ifrm5").style;
var h1 = parseInt(s1.height) - 2;
if (h1 == 0) return;
h1 = (h1<2)?2:h1;
var s2 = document.getElementById("ifrm0").style;
var h2 = parseInt(s2.height);
s1.height = (h1) + "px";
s2.height = (h2+2) + "px";
setTimeout("doChange()", 50);
}
</script>
<input type='button' value='改变' onclick='document.frames["ifrm0"].location.href="http://cn.yimg.com/i/lg/2/y_cn_lg.gif";doChange()'/>
<br />
<iframe id='ifrm5' name='ifrm5'
src="http://www.google.cn/intl/zh-CN/images/logo_cn.gif"
style='height:90px;width:500px;'
scrolling="no" border="0" frameborder="0"></iframe>
<iframe id='ifrm0' name='ifrm0'
src="http://www.baidu.com/img/sslm1_logo.gif"
style='height:200px;width:500px;'
border="0" frameborder="0" scrolling="yes"></iframe>
</body>