http://www.strille.net/tutorials/FlashXMLCompressor/index.php

The code above is preferably placed on frame 1 in the movie. You can now load compressed XML files in the same way you load normal XML files. You can still load normal XML files, just make sure you don't have any white space before the <?xml version = "1.0"?>.

exampleFLA 
例子，可以加载压缩和未被压缩的xml文件

FlashXMLCompressor
专用xml压缩工具