You Need Windows XP.
Follow this steps
1. Make a your own spray at paint or a picture.
2. Download Decal Converter. Click On this link http://barbados.plunder.com/x/$WheQqN6p2_iJrhhVRqVx5fJ0q3cqaqcC/4844c91157/?/Decal%20Converter.zip
Download it,
3. Unpack it with winrar. if you dont got winrar go to www.winrar.nl
4. Open DecalConverter.exe
5. Put your picture in the program and make your wad file on ur destkop.
6. Change the name from the wad file to: tempdecal
7. Click with your right mouse on it. and click properties then you see Read-only select that.
8. Click Ok
9. Put it in your cstrike:
Non Steam: C:\Program Files\Valve\cstrike\tempdecal.wad
Steam: C:\Program Files\Steam\SteamApps\<your email>\counter-strike\cstrike\tempdecal.wad
10. Spray at CS 1.6
Sorry for bad english
If you need better help go here. http://www.cstrike-planet.com/tutorial/2-CS-16-Spray-decals/2
Tutorial Made By : The Assasiantor