I don't have a mac.... but I can do it on PC so ill explain it for that and maybe it's close enough for you.
I assume unrar is a program you will need for mac. On windows, I have winrar and its probably just the windows version. Basically, it's a program with a compression algorithm to make a really big file really small. When the file is small, your computer doesnt know what the fuck it is, and to turn it back into the original file, you have to "extract" it with winrar (or i assume unrar(you can check this by double checking the file type that you downloaded. If it is in fact a namenamename.RAR file, then it needs to be extracted)) once there, you will have to mount the image using the above daemon tools tutorial. Then in your computer you will see a second CD drive, and in that new drive (that doesn't physically exist), you will see the disk for the expansion. You install that normally, just like any other CD and when asked for a serial use the keygen, which should ave been included in the .rar file and will appear after extraction. Move it to the gamebin? idk what that means. Something mac specific and is the name of a file directory I assume, so probably just copypasta that shit over there and play.
Sorry if you already knew everything I said. trying to help.