I just posted about a shutoff valve in my bathroom. This post is about the drain pipe for the sink in the same bathroom. It is metal, (cast iron?, rusted galvanized?). When I removed the old sink and plumbing, it revealed this pipe end (linked photo here). It is rusted on the end with the threads and part of the threads on the bottom are rusted completely off. The pipe slopes slightly downward (into the room), although I'm not sure if that was the case before I removed the plumbing, maybe it was holding it up slightly.

You can probably guess my questions...

1) Can I just attach this to pvc piping using a fernco adapter or something like it?
2) Does the rusted section of the pipe need to be cut off? -if so, best way for a diyer to do so?
3) Even worse, do I need to go into the wall for bigger repairs?

Thanks for the help. I hate the plumbing part, I just want to start laying tile, trim, etc!