How do i disable my onboard video for GA-MA78G-DS3H?

I appears that you don't disable it. It looks like this is the only setting.

It looks like that is set by default. Check it anyway, before you install the card.

Well, do i have to unistall the drivers for the onboard? and should i set the uma buffer size to disabled? And in what order should i uninstall drivers and install card ? Thanks for the reply

I have never dealt with mobos with on board graphics. I believe the UMA buffer is specifically for the on board graphics, so I suspect you can disable it. I would install the card and see if you can leave the On board driver in there and load the new driver. If you have conflicts then delete the old driver. From what I have seen, with some of the newer mobos you can actually use the discrete card along with the on board graphics for multiple monitors.

Like I said, I have no first hand experience, sorry.

Good luck.

You may be able to go into device manager (right click my computer and click properties then hit the hardware tab then click device manager) and under the "display" section, right click and select "disable" for the onboard video.

No - "display" is a monitor.
In device mgr you want Grafx adaptor.

I suggest read mobo manual for procedure - and do that. If you can't understand it - I spose you could post that here.

I'm here cos I'm curious too - this is a good question and the answer is indicative of possible good performance and perhaps other.

But really it should be in the manual - let us know  

You do not have to uninstall or disable any drivers. You need to set it up in your BIOS. (Refer to your manual on how to access your BIOS and also page 41 on how to setup the display). You need to get to Advanced BIOS Features>Init Display First>PCI Slot or PEG. If you bought a HD3400 series, you might want to set it at PEG, install the 3400 series drivers and Catalyst Control Center, and then come back to the same menu and change Surround View to ENABLED. This will allow ATI's new Hybrid Crossfire, which will give you the processing power of 2 GPUs instead of one. If you got something better then the 3400, you might have to wait until they update their BIOS to support higher end graphic cards, though I don't think it is wise to link a 3200 onboard GPU to something like the 4000 series because the 4000 might have to wait for the 3200 and pull down overall performance, but that's just a guess. Good luck

Disable that then.