This is the Xtreme G driver which includes many performance and Image Quality tweaks. These are modified NVIDIA ForceWare drivers for Windows 2000 & XP.
Modified drivers simply means that the author takes official or beta drivers from the manufacturer and starts to tweak them for either better image quality and or performance. Please bare in mind that the driver manufacturer, in this case NVIDIA, does not support drivers like these.
You use them at your own risk. For more information and dialog about these drivers I suggest you visit our forums where a dedicated section can be found on modified drivers.
HD means High Detail version. This set is based on the nVidia Forceware 71.89 WHQL drivers.