I would recommend
ZipGenius.
You extract the map files and put them in the right places.
Ex: the mapname.bsp,mapname.txt go in your server's mod's "maps" folder.
Usually you copy from their folder tree to your folder tree.
all files in "maps" -> go into -> "maps"
sprites in sprites
models in models
gfx/env in gfx/env
etc.