In the order you desire your presentatios to appear: Insert > Slides from
Files. Be sure to check off Keep Source Formatting.
Once all have been inserted, Go to Slide Show > Slide Transition. Select a
simple transition like Fade Smoothly (available in PPT 2003) the check the
box under Advance slide and enter the number of seconds you would like each
slide to appear. Select apply to all.
Go to Slide Show > Set up Show. Select Loop Continuously until Hit Esc.