With the release of Ubuntu 14.10, some of the problems related to this incompatibility issue appear to be solved. I succeeded to make both graphic cards to work as follows:
1) Install Ubuntu 14.10. In my case, I first tried updating from 14.04 but I messed up with the installation. I ended up doing a clean install from an Ubuntu CD.
2) Install the fglrx driver from "Software & Updates" -> "Additional Drivers".
3) Reboot
4) Unfortunately, the AMD Catalyst Control Center behave weirdly. The first time I run it, it did run normally. I used it to switch the card. After a reboot, the AMD Catalyst Control Center did not run anymore. To switch between cards, please follow the step 5).
5) Check whether you are using the discrete card (radeon) or the integrated one (intel) by running the in a terminal:
amdconfig --pxl
If you are using the Intel card, you should see a message like:
PowerXpress: Integrated GPU is active (Power-Saving mode).
Otherwise you will see a similar message stating that the discrete card is currently in use. To switch from using the discrete card to the integrated one, run the following command:
amdconfig --px-igpu
For the other way around, run the following command:
amdconfig --px-dgpu
In both cases you will be prompted to restart the X server. You may log out and log in again for the changes to take effect.
Best Answer
There is no need to install any drivers. Intel drivers are installed in Ubuntu by default and are regularly updated through routine system updates.
If you installed Ubuntu 14.04, not 14.04.2, you can upgrade the graphical stack including the Intel drivers and the kernel by running: