Getting Vertex Data

I''ve been searching for a long time for an effective collision detection algorithm, and I finally found one (at www.flipcode.com), but now I have another problem: I need to get the vertex information of my meshes to perform these collision tests. I know how to get data out of a vertex buffer, but I can''t use it. How am I supposed to extract multiple vertex structures from a **BYTE? All I want to do is get the coordinates of each vertex.