EDIT (the whole question, it was too unclear)
I want to use OpenSSL.NET
The OpenSSL.NET install instructions page: INSTALL
I found a solution.
Unfortunately the VS2008 C++ Redistributable package didn't work - I had to install the SP1 version AND VC++2008. The author said in a comment on its website that it was a mistake on its side, and not mine. He is currently recompiling the DLLs to be statically linked. Thank you to all of those who helped me :)