If the system is powerful enough then onboard vid should be fine. Dedicated cards these days are more for the high end gamer crowd.
That said I bought a cheapo Gigabyte NVIDIA card for $30 for my rig just to be brutally cautious. Frankly I think the thing might actually take up MORE resources. lol
I don't recall having to disable onboard video. The audio, yes. It's easy. The control panel in Win 7 is straightforward and if you want it even simpler google CNET + Win7 God Mode and it'll show you how to enable god mode in win7. It essentially gives you access to every single adjustable feature in Win 7 in a list form control panel. It's pretty awesome.
Cheers.