my guess is...the tool you have is for the newer type of cassetes...where the freewheel mech is a part of the hub and not the cassete. the cassete is mounted on the freehub and secured by the lockring....which you undo by the tool you have....
yours looks like old type mechanism where the freewheel is part of the cassete...to remove it you need different tool....
i guess this...
my guess is...the tool you have is for the newer type of cassetes...where the freewheel mech is a part of the hub and not the cassete. the cassete is mounted on the freehub and secured by the lockring....which you undo by the tool you have....
yours looks like old type mechanism where the freewheel is part of the cassete...to remove it you need different tool....
i guess this...
http://www.parktool.com/products/detail.asp?cat=4&item=FR%2D1
good luck bro