Design 3D CX 6 and 7 are fully compatible with both Vista and Windows 7. Are you logged onto the computer with an administrator's account?
Even if you are logged on with an admin account, try running the installer with the Run as Administrator option. You may also need to use this option when you launch the program for the first time, as that is when it writes its registry entries to register itself with the OS.
On Windows, being an administrator doesn’t necessarily mean you have all possible administrator privileges.
After installing the software, you may need to right-click on the executable file (Strata Design 3D CX 7.exe file) and select “Run as Administrator.” You usually only need to do this the first time you run the application. The .exe file is typically found in Local Disk C:\Program Files (x86)\Strata\Strata Design 3D CX 7\