Probably the easiest way to do this is to download the Half-Life SDK and install it somewhere on your hard disk. Download the Monster plugin source code and unzip it somewhere else. Get a GOOD file compare utility (like Beyond Compare from
www.scootersoftware.com) and use the file compare utility to compare files in the Monster plugin directory with the same file from the SDK. Then you will clearly see what had to be changed to get monsters to work from a metamod plugin.
All of this assumes that you already know C++. If you don't know C++, go learn it first (buy some books and download a free C++ compiler from
www.mingw.org to learn with). This also assumes that you already have Microsoft Visual Studio to compile the files with (if you don't you'll have a lot of trouble trying to get the files to compile with some other C++ compiler).
botman