I need to create one large lightmap for all the objects in my scene. I tried to use the "Render to Texture" option in 3dsmax 6 but the software generates a map for each object. How can I set MAX to render a single map for all the geometry?!? Thanks in advance

The way I do it is simply to temporarily attach all objects into a large one, play around with the uvw layout until satisfied, render to texture then detach into separate objects again. This assumes all your objects are editable polys or similar and you don't mind have all your origins reshuffled.