I been strugling with performance problems with cs4 and now finally I have system with stable and good performance.
I have Vista 32bit, Q6600, 4Gb, 8800GT etc...
I had very poor performance on preview monitor, sometimes it was really slow and sometimes it just didn't work at all, no image at all or no video preview, just sound.
I though that new updates for PP would help - nothing happened! But few days ago I noticed that NVidia has been released new drivers (ver.180.) and this did improve perfomance for a while, but after next boot I had same problems again. Final move was to disable aero from vista and it helped a LOT. Now AVCHD is like butter and so on, CS4 works wonderfully!
-Get latest updates from Adobe
-Get latest drivers for GPU
-Disable Vista Aero to Standard theme
-Get into work!
These are simple things to do but most of user might have not noticed these. Hope this helps!