Well, it's Vista 64 with a lot of extras, so one could assume that a minimum level of compatibility exists. I just wouldn't expect miracles. Servers are in general not meant for end-user software like PS and even the best virtualized environment cannot yet fully replace a local workstation setup. The additional background services alone could consume quite a bit of resources... Beyond that - your guess is as good as mine. Unfortunately I don't have a million floating around to try it out. ;-) Perhaps it would be best to simply run the CS4 trial on a demo machine at your hardware reseller...
Mylenium