Here's how I installed gaussian09 on a ubuntu laptop:
Unzipped the CD image (*.iso file) > extracted the *.tgz file in the "tar" directory > Copied the g09 folder to home directory > done
One can set environment variables permanently or make a setup file that one need to source each time before running gaussian. Make a text file named g09setup and write the following lines in there:
export g09root=~/
export GAUSS_SCRDIR=/tmp
source $g09root/g09/bsd/g09.profile
Now you can run gaussian using the following commands: