it's impossible to access to client's file system in web applications.
The only things you can do: upload and download. (See FileReference http://livedocs.adobe.com/flex/3/langref/flash/net/FileReference.html )
Can we use any other server side technologies like Java or php.
On server side you can use any technology you like (for handling uploading for example).
But it's also impossible to get access to client FileSystem using any server technologies.