I don't know about the CS4 running, but the HD 5850 should be fine with your spec. The PSU is a bit of a concern though. What are its +12V ratings, & does it have the required 2x dedicated 6pin PCI-E connectors?
Also note that this card is long, ~9.5" with a little to add on for the PCI-E power connectors - get a better idea at click here. G