Debris effect/horse running in office

[artistiam2]

I'm shooting a commercial and I found some green screen footage of a animal running I want to shoot. Any suggestions on how to film my actual subject? I want to show my actors sitting down and the animal running through the office.

Also how can I film debris flying through the office? Pencils, paper, pen, chairs, etc...

Thanks in advance.

And I hope this is clear enough to answer. I'm working with adobe cs4 suite.