One of the security features (PAINS) you see in Vista 64-bit is the driver signing feature. This makes it almost impossible to replace most of the systems files with modified files. Most commonly if you want to patch your TCP/IP Max Connection Limit .

You can of course disable it by Pressing F8 during system start up and selecting Turn Off Driver Signing. But then you will have to do this on every restart. So a way around this is using ReadyDriver Plus 1.1 Which was developed by someone called Uhlik.

You can download it here.
ReadyDriver Plus 1.1