Make sure that yourwindows files are updated via "Windows Update" in your taskbar.
Try manually updating your DirectX to the latest version [9.0 I believe]
http://www.microsoft.com/windows/directx/default.aspx
Completely uninstall your other installation, then reboot.
After reboot, turn of your spyware and antivirus protection. You can also disconnect your computer from the internet if you're worried about an attack during installation.
Start installing. Do not install anything more than POV and FFXI. Afterwards, reboot and then have fun updating.