Like every good demo the DemoDVD contains some hidden parts.
In the mainmenu press 5 for some young chick to explain you what demos are.
In the chapter selection on page 1 press 9 for Facts of Life by Witan.
In the chapter selection on the last page press 7 for Aphrodesiac by Acme.
In the production notes you will have to press all four arrow keys on a screen which display a picture. You will then see the unreleased demo Glitter Baby / Craw Productions. However this is really hard to find without cheating. If you know the exact screen and key sequence please mail me.
In the chapter selection on page 1 press 9 for an alpha version of Second Reality by Future Crew. use the fix
In the Credits & Greets part go to the ANSI picture of Trixter and follow the instructions of the last sentence. In case you can't read that on your screen, press left, up and enter to see Explicit by Hornet.
Many of the real demos include hidden parts too. Look at The Quasi-Official List of Demo Hidden Parts, Keys, and Tricks for an almost complete list of them.