good Luck man it's a badass game. well worth all the trouble your having now.

So you were able to get winrar installed?
If so then open the file you downloaded with winrar. it'll show you everything in the file, unpack everything to a place you can find (like c:\callofduty). after it extracts, go to that folder. You will either have a disk image (ISO, BIN and CUE etc..), or a bunch of more rar files. If it's a disk image then burn to disk, if it's more rar files, then repeat the previous step until you get a disk image.