Do embedded DLLs load server-side or client-side?

I have read on the Internet that it is possible to embed custom DLLs onto an HTML page. I would like to know whether the DLL will be loaded as a server-side process or client-side process?
The DLLs are not embedded in the HTML page, rather, a .NET Windows Forms control contained in it may be. This embedding works as part of the browser displaying the page. Therefore, it's always a client-side process. As you can guess, the client needs the .NET runtime for this to work (and most probably, be running IE).

This was first published in March 2004