how is this done? (photography)?

For 32 - 37 your camera needs to be able to take photos in rapid succession (burst mode, continuous mode), but in essence this explanation still applies:

Here is an example I made a while ago: http://www.flickr.com/photos/beetle63/5215060539/

Here is how:

Put the camera on a tripod so it will NOT move. Take photos of your subject in different spots (at first it is easiest if they don't overlap anywhere).

In Photoshop (or Elements or Gimp), start with a base photo as layer 1.

Add the next photo as a new layer #2, make bottom layer invisible (eye symbol in layers window).

Erase/mask everything except the person in #2 - you don't have to be really accurate around them as long as you left enough room between them and as long as the camera didn't move.

Make layer #2 invisible. Add layer #3 and again erase/mask everything except the person.

Now make all layers visible again and VOILA! You're done!

Once you start overlapping positions of your subject, you have to be way more accurate with the masking/erasing and with thinking about which layer needs to be in which position.

It is very important to make the subjects "interact" with each other, like for example in this photo where two of them are talking to each other, another one is chasing her "sister", etc. The interaction is what makes the photo much more realistic and believable.

For 28 - 30, I believe you are talking about the colours mostly, right? that's just a gradient overlay, found in the gradient palette in Photoshop.

For 32 - 37, here is a link explaining how to do it...

http://www.creativetechs.com/iq/photoshop_cs3s_aut...

There's one major difference, though, between that tutorial and what you want to do. That tutorial explains how to remove instances of people in different places in the frames, while you want to ADD them all together into the same frame. To do that, use "Minimum" as the stack mode instead of "Median" which is what is used in that tutorial.

I've got to run, but if I have time I'll come back and take a look at those others to see if I can figure out what effects were used.

Happy shooting!