This is probably not all that helpful, but I'm running Windows 7 Pro 64-bit and using Internet Explorer 32-bit to use the QlikView plugin without problems. My IE version is 8.0.7600.16385.
Is there an error message or something that happens when he tries to open the document? It may be worth a try to reinstall the QlikView plugin. I don't see the QlikView plugin in the Manage Add-Ons section, but it can be found in Add/Remove Programs in the Control Panel.