One of these days, I'll turn this in to an actual 
.dtx file with all of the nifty built-in auto-install
procedures, plus real documentation.  However, until 
then you have to do it by hand.

The following files should end up in your texmf tree
(or your localtexmf tree) at these locations:

   <texmf>/tex/latex/gatech-thesis/gatech-thesis.cls
   <texmf>/tex/latex/gatech-thesis/gatech-thesis-patch.sty
   <texmf>/tex/latex/gatech-thesis/gatech-thesis-losa.sty
   <texmf>/tex/latex/gatech-thesis/gatech-thesis-gloss.sty
   <texmf>/tex/latex/gatech-thesis/gatech-thesis-index.sty
   <texmf>/bibtex/bst/gatech-thesis/gatech-thesis.bst
   <texmf>/bibtex/bst/gatech-thesis/gatech-thesis-losa.bst
   <texmf>/makeindex/gatech-thesis/gatech-thesis-index.ist

Then, you need to update the file database; usually this is
something like "initexmf -u".  On MikTeX, you run the "MikTeX
Options" program, and on the "General" tab, in the "File name
database" section, click on the button that says "Refresh Now".

Alternatively, you can simply copy all of these files into your
local work directory where your thesis files will live.  
However, this is sometimes dangerous as you might be tempted
to edit them directly.  Wherever you choose to install the
official files, don't edit or modify them..

You should not need to modify the style/class files.  However,
if you find that you must modify their behavior, the best thing
to do is to copy just the section of code (e.g. the function
definition) that needs changing into your own personal,
document-specific style file, and edit it there.  You're 
version will override the "real" version -- and there is no
need to modify the standard files.

See the commented-out section at the end of 
julesverne/bellswhistles/jules-verne.sty file, which is an 
example of just this sort of thing -- it modifies the \contents
macro in gatech-thesis.cls, *without actually editing 
gatech-thesis.cls*

(NOTE: julesverne is only available from the Georgia Tech version of
the package at http://www.gradadmiss.gatech.edu/thesis.php)