What does it mean when mother sees my ghost (wearing clothing from past years) walk in house talk and then leave, when I was hundreds of miles from her at time and we were both wide awake at same time?

You can't see a ghost of a live person - live people don't have ghosts.

Some people say seeing a double foretells death but others may disagree.

This is also called a "doppelganger".

Here is a site you may find helpful:
Doppelganger! (http://paranormal.about.com/library/weekly/aa111102a.htm)

Sarah

You can actually see a livings persons spirit just like you can their energy field, likeseeing an aura.

I don't know why this happens with the living sometimes but it does, your mother probably has psychic and mediumship abilities.

Spirit can travel. There is a connection here and I believe that your mom is able to pick up on your presence. Even though you might not be there physically, I bet your spirit is there without even you realizing it.