Hi Terry,
Best practice is to try and isolate where the *.inf files started out, and set them up in the InstallShield *.ism project as Driver Installation components. Many of these drivers are supported by the DIFx runtimes that InstallShield uses from Microsoft.
For other types of drivers that DIFx doesn't handle, it might be necessary to invoke the *.inf files using SetupApi.dll (which, you can search these forums for how to wire this up, there are examples).