#1
does there exist a program that can automatically tab any song?
lol i was just wondering if such a thing existed...
#4
There are some that can tab single line melodies.
But it would have to be just a single melody. No chords, bass, drums or vocal line to confuse it.

http://www.celemony.com/cms/index.php?id=videos&tab=5#top
click EXTRACTING A GUITAR

That'll show why. That'll be as close as you can get.
There's a good chance that what I've written above is useless and if you take any of the advice it's your own fault.