From the C shell, setenv g09root "/usr/bin" or where ever 
you want it. /usr/bin is where I always put it.

cd to $g09root and unzip and untar the OPT-920X.tgz file.  
All of the G09 files will now be in the /usr/bin/g09 
directory.

chgrp -R "group" g09      I always choose the "users" group.
cd g09
./bsd/install

The only thing left to do is put the following lines 
in the .cshrc file of any user you want to run Gaussian09:
setenv g09root "/usr/bin"   (or where ever you put it)
setenv Gauss_SCRDIR "/scratch"
source $g09root/g09/bsd/g09.login

Obviously run g09 from the C shell.  It can be run from the bash shell, but 
I never have.  There is a g09.profile file in the go9/bsd directory to use 
instead of the g09.login file if you want to go that way.

I have included a sample input deck
called g09tst.com.  In the first line of this file, you can set the 
number of processors to request.  I set it to 16: %nproc=16

From the prompt type   g09 g09tst.com &
An output file (g09tst.log) and a binary file (g09tst.chk) will
be created in the same directory in which the input file is located.
In addition several temporary files will be created on the /scratch
disk.  If the job completes correctly, these files will be deleted.
If not, you must delete them manually. 

The name of the .chk file is set in the second line of the .com file,
so if you want to run more than one job at a time, either copy 
the .com file to another directory or rename the .com file and 
the .chk file inside the .com file.