NOTE: Before doing any modding, it is always a good idea to make a back-up of your game folder first.
You just need to move the files in the mod pack, into the matching folder of the vanilla game. It requires you have the 0.978e-f version, and does not work with the 'cheaty' version, if I remember correctly. For example, if you open the archive, you will see the folder, open that, there is a 'game' folder. Now if you open the folder on your hard drive where your game is saved, and open that, you will see it also has a 'game' folder. Drag the game folder from the archive into the one on your hard drive that so that it overwrites the one there already. Alternately, open the game folder in both places, and drag everything from the archive into that one. It should be fairly obvious of you look at the folder structure in both locations.