Firstly, pls refrain from making multiple posts - in particular into the same board - with the same question, one post is enough for us to find it.
Carbide.c++ Express uses the Nokia X86 compiler, also known as the "WINSCW compiler", for emulator builds and whatever compiler that comes with the SDKs for target builds (depends on SDK). The X86 compiler comes with Carbide.c++ Express so there is no need to install CW to use Carbide.c++. However, the installation does not make the X86 compiler available for use by other tools, therefore for instance it does not become available for S60 3.0 command line building by default (the 3.0 SDK no longer comes with an X86 compiler).
But then the whole point of Carbide.c++ Express is that you can now move from command line to being much more productive with the IDE so I see no reason to use command line as long as Carbide meets your needs (eg in terms of supported target types etc). And if your needs are not met, then this means that for the time being CodeWarrior is the correct tool for you and you just have to wait a little longer for Carbide.c++ Developer Edition to move to Eclipse/Carbide.