WindowFX performance is totally reliant on Video Cards and drivers.
Nvidia is working on some drivers for the Geforce 4 that will help.
ATI's drivers are *usually* better but they seem to keep breaking things.
The newer cards have better drivers.
I've been running it on a Geforce 4 at home without a noticeable slow down,
but results vary. It also depends on how many of the options you have
running at once since a lot of them are heavy animations, they will logically
have a resource impact.
