They are both nVidia chipsets, so the driver is identical and will make the necessary changes automatically. However, you need to tell X to start using the alternate chipset. The quickest way of doing this is disable the onboard GPU in BIOS (it must be disabled, not merely changed in priority) if this is possible with your BIOS. Then reboot, and hold Shift down whilst the Kubuntu loader screen is progressing. This will throw you into the AV Wizard again which will choose the correct chipset. However, as you are connected using Svideo, you will need to use the keyboard shortcuts to select that output once the AV Wizard is running (keys 1 - 5, can't remember which is svideo, but make sure you wait at least 15 second between each attempt)
If your BIOS does not have the ability to disable the onboard, then you will need to ESC during the GRUB boot menu, and go to the recovery console. From there you can type:
Now identify the PCI BUS ID of the new chipset. Then edit your /etc/X11/xorg.conf file, and modify the PCI Bus ID parameter in the Device section to match..., save, reboot, and hold shift down again.