I know Matrix and Monty Python come in installers (I wrote them
), so if Simpsons and South Park are packaged in EXEs too, then just run the EXE.
However, and I suspect this is the case, they come as the raw DLL. This needs to be placed in the Plugins folder (which you seem to have done), and any accompanying .reg files need to be placed in the same place and run.
Any German translators out there: feel free to translate this post.