Required: Cs background maker
download from here: http://adf.ly/oX0mR
Step 1: open cs background maker
Step 2: Load any image you like
Step 3: select resolution (800x600)
Step 4: Click Save background on any folder
Open that folder where you save the background.
Copy the background folder and txt file.
paste on Counter-strike/cstrike/resource
Done :)
Video tutorial : https://www.youtube.com/watch?v=F5-oGniLJew