From VFXPedia

Running Fusion 5 and later on Windows 64 bit

eyeon now offers a 64 bit version of Fusion and Rnode to subscription members. For more information, log into your eyeon account and download the update.

The 32 bit version of Fusion 5 can be used on Windows 64 bit Edition, and benefits from greater available memory (up to 4 GB). The increased address space that Win64 can use also provides benefits to Fusion even on systems with less memory.

However, not all Fusion features may be available - not all video hardware vendors provide 64 bit drivers yet, and QuickTime has not been released for Win64 at this time.

Running DF4 on Windows 64 bit

There are two important issues to be aware of when attempting to run DF4 on a Win64 machine.

DF4 will not recognize the Hasp dongle under Win64. However, if you have a network license server, network licensing may be used in place of the dongle.

Certain functions in DF4, most notably Matte Gamma controls, will produce incorrect output when running on an Intel CPU under Win64. This may cause significant artifacts when rendering some flows. No artifacts occur when running on AMD CPUs, and Fusion 5 or later versions do not have this issue.