PLEASE HELP, PLEASE PRETTY PLEASE

Can someone tell me how to unwrap a JSObject that I pass into
XPCom/XPConnect

For example: 

netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");


const nsISupportsArray = Components.interfaces.nsISupportsArray; 

var x = Components.classes["@mozilla.org/supports-array;1"].createInstance(nsISupportsArray);

var y = new Object(); 
y.foo = "Hello XPConnect!"; 

x.Append(y); 

//NOW I WANT TO GET MY OBJECT BACK!!! 

var z = x.GetElementAt(0); 

alert(z) //displays [xpconnect wrapper nsISupports] 
alert(z.foo) //undefined ?????????? WHY???????? 

Thanx 
Sean 
[email protected]