Wow, you don’t ask for much, do you?
If you’ve never used the program before, it’s gonna take some work. I’m not even sure if your version has the same particle system as the latest, but I’ll give you a thumbnail sketch of what you’ll need to do.
First, animate your characters, figure out where their feets is going to be planted with each step. Then place a particle emitter there. I suppose you might be able to get away with just one and move it to the different locations, but anyway…
Then set it to eject spheres, and you’ll have to texture them to look like sand. Anyway, figure out what frames your feet are going to hit the ground, and set “Emitter on NOW” at that frame, and set it off a few frames later. Then set it to eject thousands of particles at a high rate, maybe 5 ft/sec or something. Set the emitter size to be maybe the size of a human foot.
Then place each emitter just at the surface, set them all to Die on Impact. Then run the sim, and then tweak as necessary. I’m probably forgetting something, so you’ll have to mess around a bit.
You’ll also want to do some motion blur, either in Carrara (takes forever, not very good) or in After Effects or something else. If you don’t do motion blur it’ll look real bad.
Then you’re gonna have to set a deformer to deform the sand as each foot sinks down, but you can save that for later.