problems creating the sims3.ISO file.

I have a simple question. I downloaded the torrent from your site for The Sims 3, downloaded it, used stuffit expander and placed both of the ISO files on my desktop. the next step is to go to the terminal and type in the two codes to combine the two ISO files together. when I input the codes and press enter it wont create the new file on the desktop like it should, instead it tells me that "no such file or directory"( referring to the 2 ISO files). I've tried different variations of typing the command in the terminal. (atleast 2 hours spent). I'm pretty good with computers and the instructions are easy to follow, so I'm really confused on whats preventing me from creating the ISO file. Please help

//EDIT

Model Identifier: MacBook1,1
Processor Name: Intel Core Duo
Processor Speed: 2 GHz
Number Of Processors: 1
Total Number Of Cores: 2
(i'm working with a leopard, could the problem be my computer?)