A single install will work just fine.

Keep in mind there are Features in InstallShield which need to be logically separated. For example, some of your tables maybe used for the application which you want to overwrite everytime and other tables is used for capturing data from the user. Each of these are considered different features with different properties.

There is a location in InstallShield which will allow the user to select where the EXE is to be stored and another where the Database is to be stored.

I use an INI file which would be located on the local machine to find the database. The INI file can be defined in InstallShield which will point to the DatabaseDirectory variable.

e.g. c:\winnt\application.ini

[FileLocations]
DataDir=F:\blah\blah2\blah3\dat

When the user selects the EXE directory, it would be something like C:\Application\bin for a local install and f:\blah\Application\bin for a server install.

When the user selects the data directory, it will be F:\blah\blah2\blah3\dat which will be saved to your INI file. Your application only needs to get the information from c:\winnt\application.ini.

An alternate approach is to use the Registry; but users don't know how to go into it to tell you where they installed the data!