Teleporters are always good to use in science-fiction games. They are useable for both single-player and for multi-player. They are really simple to create aswell.
http://www.mnemic.tk/education/videotut ... o_tscc.rar
Size:3.61Mb
Length:1:22 Minutes

Hi there,
I'm desperately looking for a way to make elevators and simply to use platforms. The tutorials are not playable with microsoft, nor with quicktime. How do I fix that?

Oh, but they are =)
you just need a CODEC (codec are like, drivers for videos and movies)..
http://www.techsmith.com/products/studi ... wnload.asp
there's the one you will need, it's free and very very tiny.
http://www.mnemic.tk has one on platforms,
http://www.modsonline.com has 2 on platforms and one on complicated elevators.