Addon confirm folder replace extraction problem

hi, i have this problem with extracting gmod addons, for some downloads, when i extract them a popup shows up and it says this

Confirm folder replace
this destination already contains a folder named “materials”
do you still want to merge this folder

date created: 3/6/2011

with this one?

type: file folder
date modified: 5/22/2008

oh, and by the way, i use winzip

Click Yes if you want the addon materials along with your materials.

if i press “yes” the addon will not show up in gmod