These are the new HD models, sounds and sprites that came with the update.
These files are intended for those who are to lazy to reinstall the game.
Place the "valve_hd" extracted folder to this location:
C:\Program Files (x86)\Steam\steamapps\common\Half-Life
These files are intended for those who are to lazy to reinstall the game.
Place the "valve_hd" extracted folder to this location:
C:\Program Files (x86)\Steam\steamapps\common\Half-Life