Some points, I can explain:

1) There are some Libaries from Microsoft that were commonly used. One Library is "Microsoft Foundation Classes" short MFC. They exist in multiple version. Most commonly used are 4.2, 7.0 and the newest is 7.1 I think.
When a product uses them, they will normaly install it through a redistribution-pack from microsoft. They install under system32 directroy. (So it is ok)

2) That error message from conitec simple means, that the DLL cannot be used. This could be, because the DLL is not valid or that some requirements are not available. The a6mysql.dll needs the libmysql.dll. My own DLL, that I am writing at the moment, needs 2 Libs (pthreads and HawkNL).

When you look at the MFC-DLLs, you will see, that the version is available inside the name. mfc42* (4.2) mfc70* (7.0) and so on.
The libmysql.dll has no version in it's name, but you can be sure, that there are different versions available. And you got another installer than me. So I think, that you are using a different Version than me and the author.

I am using mysql-4.1.10-win32.zip from mysql.com. So maybe it works for you with this DLL.

Destop: Could you add the libmysql.dll in your zip File? So that all requirements are met with your distribution? Thank you in advance!

I hope, that this helps a little. If you want, I can send you my libmysql.dll (1MB only unzipped).

With kind regards,

Konrad