If the installer doesnt work, put these files in manually. Otherwise, use the installers!

they go in
Lionhead Studios\Black & White 2\Data\ctr\b*

the star is the name of the creature that you want the turtle to replace.
so if say you wanted the turtle to replace the wolf, you'd put these files into the bwolf folder.
to see further installation instructions, go to the "Manual Instructions" file in the Files_1 
folder if you havent already

to uninstall, delete the delete all files starting with t_turtle in the b* folders. To see
further instructions, go to the "Manual Instructions" file if you havent already.

Enjoy!
