Demos and Openings
I found these videos on YouTube and posted them here for your convenience, all in one place. They show only the first few minutes of each game, promo or demo, but they do let you get the flavor, if not a whole meal. Bon appétit!
Complete Screenshot "Movies"
Here are complete playthroughs in an unusual format: hundreds of screenshots showing every move, every text input, every line of dialogue... everything! It's not as good as playing the games, but it does give you a good indication of what they were like. And these are complete, from beginning to end!
Download these ZIP files by right-clicking on the link and choosing "Save As..." from the resulting menu. Unzip them into a folder somewhere, open that folder, and view the first image in your favorite image viewing program (I strongly recommend Irfanview, available for free here). Then press the right arrow key to see the next screenshot, and the next, and the next.
Warning: These are large files, ranging from 21MB to 278MB!