Qt is shipped as part of the Maemo 5 SDK. See the Qt for Maemo 5 Requirements document for details about installing the Maemo 5 SDK.
Once the SDK is up and running, install the libqt4-dev package to get the Qt libraries, headers and build tools.
To install the Qt for Maemo 5 examples, install the libqt4-examples package.
For more information about building and running Qt programs on Maemo 5, see The Maemo 5 Platform - Introduction to Qt.
We hope you will enjoy using Qt.