theres a few ways to do this.
to do it as the computer boots up, put the line in
to do it as one user logs in (ie you) put it in ~/.bashrc (thats the file called .bashrc in your home folder)
theres a line that says something along the lines of
#User specific aliases and functions
<put it here>
the final way is to put it in the file that is parsed when all users log in. its somewhere in /etc, i can't recall its name
Hope this helps anyway