In step 1, select they type of computer you have. If it is a box with a separate screen, select desktop. If the screen is attached to your computer by a hinge, select laptop.
In step 2, select Radeon HD
In step 3, select Radeon HD 5xxx
In step 4, select the OS you are currently running, if you do not know, you would have to find out first.
ATi is owned by AMD now, so the drivers are from AMD's site.