Model view to world coordinates?

After doing various function calls and large amounts of calculations, i finally get to the stage of drawing an object. Along with the object, i draw out its bounding box.

The result is perfect, however now i need to do collision detection. I've worked out the equations i'm going to use for this, but first i need the global coordinates of the vertices of the bounding box.

Basically, when i have code that says:

GL.Begin(BeginMode.Lines);
GL.Vertex(4, 2, 1);
GL.Vertex(2, 3, 7);
GL.End();

how can i get those coordinates out of the model matrix, and into global coordinates?

Thanks for any help!