Although Matty is correct that you wont get the cascading submenu on Vista/Win7 (because they don't support it anymore), you should be presented with a dialog where you can pick your contacts when you click on your email address.
Can you tell us the exact version of the script and also what the exact command line is behind that item in the menu?
Also, is the preferences menu, the second option to
"Display all online contacts" should be disabled if you use Vista/Win7. If it is not, you either are using an old version or it doesn't recognize Win7 64bits properly.
You'll fnd the version number in the about window of the script.
It should be 2.4.2. If not, download the
latest version from the official scripting database.
The command line can be accessed if you right click that menu item (your email address) and choose properties.
Though, it could be one of those incompatibilities of 64bits which I can't check myself (I don't have Win7 64bits).