Creating an enviroment variable will ease the process of extracting skins, maps, and things like that.
Find out where your cstrike folder is.
The default directory for your cstrike folder is this: C:\Program Files\Valve\Steam\SteamApps\username\counter-strike source\cstrike\
the username field may be replaced with your steam login name.
Once you find your cstrike folder copy it (control+C) to your clipboard.
Go to Start>Control Panel>System
Click the "Advanced" tab.
Click "Environment Variables"
Looking at the top half of the new window, click "New".
Give the variable name cstrike
Paste (control+V) the directory name as the environment VALUE and click OK.
Keep clicking OK until you are out of the System window.
You may be wondering what this actually does, and here is a test for you to find out:
Press Start>Run
Type in %cstrike%
You should now see your cstrike folder for counter-strike source
When are you ever going to use this?
If you downloaded a skin and it came with materials, models, scripts, and sound, or just maps folders (AS THE FIRST SET OF FOLDERS), check this out:
Open up notepad and paste this:
cd %cstrike%
"C:\Progra~1\Winrar\unrar.exe" x -o+ %1 materials\* models\* scripts\* sound\* "%cstrike%"
pause
(Assuming you installed winrar there)
Save it as "extract to cstrike.bat" or whatever you want (just make sure it is .bat.)
Drag and drop the rar file into the bat file and it will extract the skin/map/gui for you.
This won't work for all skins since some smart people will try to be unique or something and pack their release without seeing materials, models, scripts, and weapons first.
Watch out, readme files and screenshots may get extracted too! Maybe it's better to stick to my Installing CSS Skins tutorial.