Systems requirements require 1 GB of RAM or more and the question remains why doesn’t the Adobe software recognize the RAM.
Go to the Apple menu and the Abut this Mac and see if it recognizes the RAM if it says you have 1GB of RAM as you say have install and I am certain you do, then click on the more info in the about this Mac dialog and then go to the Memory section and see if it says all the RAM is OK. If so I would say there is an issue and it does sound to me to be an issue.
The only question that would remain is what that issue.
Perhaps an undetected memory leak, what computer model are you trying to install it on?
Is it a newer MacPro? I am just speculating it could be a bad system install that is first showing up or it could be that you came across a memory leak that then may have found it way into CS 4.
I t would be interesting to see your configuration and hardware are, btw where di dyou get your RAM?