The lime screen backdrop used in todays movies FX to put characters in fantacy worlds, is that possible to do in Poser?  Does anyone have a tutorial (script ) to delete the lime colored backdrop to get the effect?

You do this using highend video editing software, you can create a scene in Poser with a Green Background that the video editor can replace with something else.

Attached Link: http://www.sparkyworld.co.uk/3d7own.htm

Set the poser background colour as "lime green" - render your poser movie and import it into your video editing software. In your video editor load your main clip - then import the poser clip as a 2nd 'track', find the chromakey option use the colour picking tool to select the green. Now play :)

Pinnacle studio is reasonably priced about 40UKP and can do this moderately OK. 

Sometimes if you anti-alias the render the video can have the fuzzies around the edges - espically with hair. If that happens try exporting the "video" from poser as a series of .PNG images and flood fill the white areas with the green -  warning it's bl**dy boring doing 400 frames this way :)

If you're working with Mini DV watch the poser render size and framerates (it's a b*gger to line them up right) 

The simplest way is to import the video clip as a video background within Poser. 
You can also aplly video as a texture (say to an plane) in Poser 5 and higher
Stick with .AVI as there video codec issues. 
  
Have a look at my tutorial (link above) for some fun ideas about using video within Poser.

You can achieve the same results rendering your frames to .PNG or .TGA that has an alpha channel and then compiling the frames using the alpha as a mask. Or as mrsparky suggested, import the video as a background directly into Poser.
Not necessary to go green ;>

I have found that if you render  the video as un uncompressed avi file using firefly, that if acts the same as if you rendered it as a png. It retains alpha transparency which some video editing programs recognize (I use Ulead Video Studio). It saves you having to render each frame individually. Works best with shortish clips or if you have alot of hard drive space.

That's a good observation. I would certainly recommend keeping .avi's uncompressed until the absolute final. and even then keep an uncompressed version on hand.

Still, (except for maybe very short clips), it's best to render to individual frames to start off with. If something unexpected should happen somewhere in the middle of the rendering process, you still have the rendered frames up to the point of the problem, so you don't lose everything and have to re-render right from the start all over again ;)