What's a good way to make a matte so i can composite my Poser Dinos into my video?

Attached Link: http://www.thugsatbay.com/tab/?q=zweistein

If you render your animation as seperate screens and save them as png files, they will have alpha channels saved with them, then you can use zwei stein or wax or virtualdub to combine them with your video. Using zwei stein you can make the background a colour and combine the videos like chromakey. Zwei stein is free at the link.

I dont quite understand what you mean: What i want to do is get my animated Dinosaurs (or anything for that matter) to go behind somthing like a person or a tree.

Had the same problem myself and figured out a workaround, so try this tutorial (PDF)... Using Alpha Planes in Animation Tutorial http://www.sparkyworld.co.uk/3d7own.htm

Sorry I thought you wanted the background as video with the poser objects in front.

If you want to create a matte for live footage, you'll need an app such as After Effects or Combustion. Try MrSparky's tutorial as a good work-around.