As far as I know you can't remove materials, you'll have to restart Poser to do that. I've seen P4 on the Mac complain that it doesn't find textures and bump maps when it doesn't have enough memory allotted to it, but 1 gig seems to be rather much. Maybe you could try to reduce the size of some texture? Also you could try making things invisible, like if M3 has clothes, try making the covered bodyparts invisible.