Follow the steps below for speed hack in cs 1.6:

1. First download and install Cheat Engine from here.
2. Start your CS 1.6 / Condition zero/ CS Source.
3. Run cheat engine.exe file.
4. Now open the list of running processes by clicking on the first icon in the toolbar
5. In the process list search for your game process. Select it and click on open.
6. After opening the process check the “Enable Speedhack” option. Drag the arrow on the bar to increase the game speed.
7. Now go to your game and see the difference