You do not state what type of installer you are using.
I have an installer that contains files for a server install, and files for client install. It also has files that are common to all.
I am using a basic MSI install. In my project I have one main Feature for all common files. Under this feature I have a feature for Server and a feature for Client. I set conditions on the feature InstallLevel so that only one or the other can be installed. As added insurance, for my server specific files, I add a component condition, and likewise for client specific components.
In my UI for the installer, I have a "feature dialog" that only allows the user to select one or the other feature. I happen to use radio buttons, but you could use simple button controls in place of your navigation buttons. For instance, instead of the user clicking 'Next' to continue, they would click "Server" or "Client". How you accomplish this is up to you, but behind the scenes you are setting appropriate property values that get evaluated for the features.
Finally, I have a number of custom actions that only run on a server install, and so for these I utilize the same property check as I do for my feature Install Level settings.
