This may help if you want to have "Disable internal pointing device when external USB pointing device is attached" option in the synaptics control panel without having to install a different touchpad driver:
Open regedit and go to HKEY_LOCAL_MACHINE\SOFTWARE\Synaptics\SynTPEnh, right click and select New > DWORD (32-bit) Value and name it "DisableIntPDFeature". Modify its value to 33 in hexadecimal, or 51 in decimal.
Additionally, you may need to make similar modification(s) under HKEY_CURRENT_USER, but the above modification was sufficient for me.