How do I import mx.core.* with CS4?

[Alluvian]

Is mx.core.* something in the flex sdk / framework?

I am trying to get the unserializer from http://www.sephiroth.it/test/unserializer/ to work with flash CS4, and I am getting the compiler error:

1004: Namespace was not found or is not a compile-time constant.

The lines called out in the package are:
use namespace mx_internal
and
mx_internal static var c:uint;

I don't know the first thing about namespaces, but does anyone know how to get this package/class working in CS4 AS3? It might be something simple I am missing.

I have attached the .as package file (uploaded as a txt file) if anyone wants a look...

Any help would be appreciated. I am having to get a lot of lists from a mySQL database and it is becoming a real pain urlencoding them all manually. If I could just urlencode(serialize($result)); in php and send that file to AS3 to be decode it would be so much simpler.