Download Winrar from
Here
Once you have done that and installed winrar, Right click the file that is zipped then choose to Open With Winrar. It will then ask you where you want the files to be placed, Just place them onto your desktop for now.
Once you have unzipped the files you wanted unzipped, Just place your graphics into the following directories:
Kits:
My Documents/Sports Interactive/Football Manager 2008/Graphics/Kits
Logos:
My Documents/Sports Interactive/Football Manager 2008/Graphics/Logos
Faces:
My Documents/Sports Interactive/Football Manager 2008/Graphics/Players
Backgrounds:
My Documents/Sports Interactive/Football Manager 2008/Graphics/Backgrounds
Balls:
My Documents/Sports Interactive/Football Manager 2008/Graphics/Pitch/Balls
Nets:
My Documents/Sports Interactive/Football Manager 2008/Graphics/Pitch/Nets
Dugouts:
My Documents/Sports Interactive/Football Manager 2008/Graphics/Pitch/Dugouts
I don't know what you have downloaded but you get the picture.