Visualization - transparency of solid elements

I'm trying to check penetration between two solid parts. I have two questions, the answers to which will help me visually identify penetration more easily:
1) How do you change the transparency of a part with solid elements? The geometry transparency option on the visualization toolbar only changes the transparency for surfaces, not solid elements.
2) Is it possible to view some parts as shaded and others as wireframe at the same time?

Thanks.