You can build installers for any supported platform on any platform it is running on - so you can build Windows, Linux 32bit, Linux 64bit, and OSX from Windows.
In order to build a Linux installer, simply add all files (libraries, binaries and other files) to the project. Then, build the installer for Linux and it will deploy the application.
The main issue with building Linux installers on Windows is that permissions are not properly preserved. However, the default permissions for all files are 0755, which makes the files executable.
Regarding Symbian, InstallBuilder for Qt does not allow deploying software for this platform. Curently, the only addition is a new Qt-based frontend allowing you to present the same familiar interface as the software being installed.
