How do you download 3d drivers

If by 3D Drivers you mean the drivers for your graphics card, check the site of the maker of your card usually ATI or Nvidia.
ATI: http://ati.amd.com/

NVidia: http://www.nvidia.com/page/home.HTML ).

If you need DirectX you can find it on the Microsoft site or here:
10 (vista) http://www.gamesforwindows.com/en-US/AboutGFW/Pages/DirectX10.aspx
9 (xp and earlier) http://www.Microsoft.com/downloads/details.aspx?FamilyID=2da43d38-db71-4c1b-bc6a-9b6652cd92a3&DisplayLang=en