Without knowing a lot more information about your project, your render settings and what you are doing it is impossible to diagnose your problem. It's like going to the doctor and saying to him I don't feel well, then not answering any questions and leaving the office before you are examined.
What are your comp settings?
How are you previewing?
What are your render settings?
Define "shake" - is it a rapid jittering, a stuttery motion when it's moving sideways, a slow jiggle?
Any chance of an example video? Or (at the very least) some screenshots of your timeline and comp?
What exact version of AE CS4 are you using? 9.0.3? 9.0.1?
What are your other system specs?
What's your experience level with AE?