1. download the demos. The hardocp benchmarks are available in the half life 2 sticky thread. I'm not sure where Anand's benchmarks are available for download.
2. extract the files into your half-life 2\hl2 directory
3. create a shortcut to hl2.exe and add the following to the shortcut properties after ...\hl2.exe" in the target section:
-mat_preloadshaders -preload -console -toconsole -width 1024 -height 768 +timedemoquit hardocptimedemo_canals_09
change 1024, 768 to the desired resolution and hardocptimedemo_canals_09 to whichever demo you want to run
4. double click the shortcut to start the benchmark. Your results will be in the half-life 2\hl2 directory, a csv file named sourcebench.csv.
If you want to use AA/AF, run the unmodified shortcut and make those changes and exit or edit the cfg file.