Copy the ID1 folder with contents from the Quake installation folder (or the installation CD) into the DarkPlaces folder, in this example you'll end up with c:\games\quakedp\ID1.
Copy the contents from the downloaded zip file to an empty folder of choice, in this example c:\games\quakedp.
Windows 64 bits: DarkPlaces engine Windows 64 OpenGL build 20140513.
Windows 32 bits: DarkPlaces engine Windows OpenGL build 20140513.
Download the latest stable/official release of the DarkPlaces Quake engine files:.
Installation of the DarkPlaces Quake engine
You don't have the original Quake game? Download Quake (including Mission Pack 1 and 2)!.
The game files are in the ID1 folder on the CD.
If you have an original Quake CD with a Windows version, you don't have to install the game.
The game files are in the ID1 folder of the Quake installation. Instructions on how to install a game from CD in DOSBox are here.
If you have an original Quake CD with a DOS version, install the game with DOSBox.