Nevermind, I've got it. Putting the server file in \Tekkit\mods and the client file in C:\Users\XYZ\AppData\Roaming\.techniclauncher\tekkit\mods worked straight away for me. I also added 'mod_Forestry=on' into the Mod Select file, but I don't know if that's necessary or not.
Can someone explain to me exactly what to do with these please? I get that you should put a 'z' in front of the file so that it loads last, but where exactly are these files meant to be placed? I actually have no idea where the client directory for the technic launcher is, so please be precise. Thanks. :)