I have a machine with similar specs to yours which I have set to HQ mode without any hiccups.
Amd Phenom II 550 @ 3.1 ~ basically the same as yours
Ram 4GB ~ 1.5GB in use with firebox open in the background with windows 7 , - so you're 2GB will be fine.
Asus motherboard
Amd Radeon HD 6850 ~ granted it's a lot faster than your card. - Although yours is still far from being an on-board graphics solution so I'm 99% sure you'll be fine here.
Typically my cpu usage sits under 25% when I'm watching videos, so I'm not exactly taxing the system either.
