I have seen problems with installing CS3 applications after installing CS4 applications. Installing in the other order works fine.
Is there a way that I could run both without uninstalling the cs4 suite?
No. There is a technote on this somewhere on the knowledge base. If I recall correctly, it hinges on several shared components such as the PDF libraries and a few other things. The thing is, if the older CS3 version is detected, the CS4 installer will leave it in place, but if CS4 is installed before CS3, it won#t allow the older components to be installed, as they would potentially overwrite CS4 components, rendering it defunct.