I myself have not tried it, but do you try also the Windows XP mode to open NAV in that Windows 7?
Please share to us the result. Thank you.
These are some readings:
What is Windows XP Mode?
Windows XP Mode for Windows 7 makes it easy to install and run many Windows XP productivity applications directly from your Windows 7-based PC. It utilizes virtualization technology, such as Windows Virtual PC, to provide a virtual Windows XP environment for Windows 7. http://www.microsoft.com/windows/virtual-pc/get-started.aspx
Secret No More: Revealing Windows XP Mode for Windows 7