ATI is the GPU manufacturer (graphics processing unit), sort of like AMD and Intel are for CPUs.
If this is the computer you have (http://h10025.www1.hp.com/ewfrf/wc/softwareList?os=228&lc=en&dlc=en&cc=us&product=3192878&lang=en) then the only drivers available are those listed under the link.
To fix your VGA driver issue, try downloading the drivers for your specific graphics card from ATI's website.
What's the model of your graphics card?