Drupal 7 Site for Displaying PPT or JPG
There are many, many ways to do this in Drupal but I'll outline two basic approaches for D7.

First, you'll definitely have a much easier time working with .jpg than .ppt.  As Drupal is open source, it supports open file formats (jpg) much better than proprietary ones (ppt).

Warning: this is not a complete tutorial; writing one would have far too many steps and is out of scope for this site.

APPROACH 1

Views Slideshow:  This relies on the Views module.  If you're new to Drupal, you should definitely learn how to use Views first; Node One has an excellent tutorial on Views.  Using Views slideshow, you would roughly do the following: 


Create a content type for your images.
Create a vocabulary Categories using the Taxonomy module and add each individual category as a term.
Create a node of content type image for each picture.
Configure Views Slideshow to show each gallery on its own page.


Why use this approach?  Each picture will be its own node.  This allows you to later add different fields to each picture such as a rating (with Fivestar) or the name of the photographer, etc.

APPROACH 2

Field Slideshow: This approach allows you to store all of the pictures for each gallery on a single node.  To do this:


Create a content type for galleries and add a field to hold the pictures.  Make sure it allows for multiple values.
Create a node of content type gallery for each category.
Configure Field Slideshow.


Why use this approach?  It is somewhat simpler to set up and requires less tinkering with Views.  However, it is less flexible.