Place all the contents of all three .zip files in the same directory.  Double click on the .exe and select the main BG2 directory as the destination folder. 

Go there and double click on the setup-wererat.exe file.  Choose yes to install.

In the game, go somewhere suitable (the docks, slums, someplace like that -- any largish map where the wererats can move around a bit) and CLUAConsole:CreateCreature("ajWRat01") to create the creatures.

GB