The
3D menu holds commands for working with 3D files. I can't tell you much more than that from personal experience, since I don't work with 3D files in Photoshop, but there's a good overview here:
Adobe Photoshop CS4 * 3D and technical imaging
As to why it's crashing...hmm, I don't know. Does it crash completely (i.e. throw you out of the program) or do you get any error messages? Have you tried resetting your Photoshop preferences? Is everything else working OK? Have you recently installed any 3rd-party plugins?