DOM XML: retrieving value

I'm using Ajax in a website and suppose I have got the following XML string from the server:
<root>
<a>
<aa>Text</aa>
<bb>Text</bb>
<cc>Text</cc>
</a>
<a>
<aa>Text</aa>
<bb>Text</bb>
<cc>Text</cc>
</a>
.
.
.
</root>
I do not know how many <a> elements are there. Suppose, var x contains the above XML data. So my code is like:
var x = xmlHttp.responseXML.getElementsByTagName("aa");
I want to extract those Text inside children of <a>. I tried x[i].childNodes[i].nodeValue. But they are showing empty string. How can I extract those text? Please help.
[824 byte] By [Donotalo] at [2007-11-20 9:51:13]