It is assumed that you have completed the installation process.
If the installation has worked, then any 3D application should work without issue. A simple way to verify without any possibility of failure is to verify the following occurs. Please note that you may have needed to go through distribution specific process to enable the 3D support.
$ fglrxinfo display: :0.0 screen: 0 OpenGL vendor string: ATI Technologies Inc. OpenGL renderer string: MOBILITY RADEON 9700 Generic OpenGL version string: 2.0.5804 (8.25.0)
You can also run the ATI provided application called fgl_glxgears which should show a spinning cube with the venerable glxgears running on each face.
You can now move on to configuring the driver.