Constraining a movieclip to the bottom of browser?

Ok this is an effect many websites employ, but I’m unsure on how to accomplish it. One that comes to mind is
http://www.chromazone-imaging.co.uk/flashindex.html

Nevermind the sweet background effect, that’s for another day. See how the logo at the bottom right is always constrained to the bottom when you resize the browser? That’s what I would like to do. I’d like to have a movieclip that will slide in at the start, then wherever it slides in to (depending on which button is pressed) It will stick there, relative to the bottom of the browser. Any help would be appreciated! Thanks!

_Filmguy15