-Made by ForoY-

okej this is how you install the 
background

1. Extract the file

2. Go to C:\Program\Steam\steamapps\"Your Steam Name"\counter-strike source\cstrike\materials

3. Make a folder called "console" (if you don't allready have one)

4. put the "background01" in there and it should work

Note: If it still does'nt work try
to mane the file to "background01_widescreen" insteed (it worked for me)