All Half Life 2 demos must reside in the C:\Program Files\Valve\Steam\SteamApps\username\half-life 2\hl2\ directory.
Once Half Life 2 loads, simply type timedemo followed by the name of the demo file you would like to run.
To run a Half Life 2 timedemo you must first modify your Half Life 2 shortcut to include the -console switch then launch the game. Unlike Doom 3, Half Life 2 has no build in benchmark demo but it has full benchmark functionality.
