look the Premiere Pro CS4 what you have x64 or x32 bit?
I have Windows 7 Home Premium 64bit.
I have installed the latest nVidia drivers for the Quadro FX1800.
This only happens when I am working with Premiere Pro cs4.
I also have a Matrox MX02 Mini for outputting to an HDMI monitor, so I set up Projects using the Matrox Presets. When I set up a non-Matrox Project the video runs smoother, but most things like simple Cross Dissolve transitions and using key frames to fade in or out require rendering.