> Hi, I have mac os operating system 10.7.3 and I'm
> very clumsy with handling code. I have followed your
> instructions in terminal, but I have not been able
> to install the program I downloaded from their
> website

You need to install either homebrew or macports:
<http://mxcl.github.io/homebrew/>
<http://www.macports.org/install.php>

Once installed, you just have to run in a terminal:
brew install httrack
or, for macports:
sudo port install httrack 

MacPorts is the first project, and homebrew is more recent (if I am not
mistaken) one.

In all cases you'll have to install Xcode and related build tools (this is
probably simpler with homebrew for beginners - there is some kind of automated
script).

[ Please note that unfortunately I only have access to an unofficial machine
for minimalistic tests, so I won't be able to reply to all questions regarding
OSX ]