Disabling via BIOS option

Some computers have a BIOS option to disable the onboard graphics.

On boot, press your BIOS key and look for a graphics option you can disable.

Disabling via Blacklisting

If there is no BIOS option, you'll need to blacklist the onboard graphics by putting your kernel module that is loaded for your onboard graphics into the /etc/modprobe.d/blacklist.conf file.

ATI graphics usually load the fglrx kernel module.

N.B. if you run lsmod you should see what kernel modules are loaded. This will include any graphics kernel modules. You should see fglrx as being loaded for your integrated graphics.

Choose Accessories - Terminal and then type in the terminal

sudo nano /etc/modprobe.d/blacklist.conf

This will open a text editor with the contents of the current blacklisted kernel modules. Add at the end

blacklist fglrx

Save and reboot.

If you re-run lsmod then it should show that the kernel module fglrx is no longer being loaded. That means your integrated graphics is now disabled.

Setting your NVIDIA Card resolutions

As to your NVIDIA resolutions - have you activated any hardware drivers in the Administrator - Additional Hardware drivers window?

You'll need to run nvidia-settings to adjust your resolution when the driver is installed.

Type in the terminal

gksudo nvidia-settings