no
Preferences -> Itunes sharing
you can og into your itunes account from the other computer
you cant unless it was a library with an account
Music from iTunes is for your own personal use. You can have it on your own computers but it is illegal to redistribute it to other people.
An Itunes account is free
Yes.
you can't. you can only get games on itunes if you have an account.
One can create another account in the other country and authorize your iTunes stores to access movies, songs and apps.
I suggest you reinstall ur iTunes, and then reset ur iTunes account password to see if you can log into itunes. If it still doesn't work. You can create a new iTunes account. Hope it helps.
That might have happened because apps or music on your iPod were downloaded with another iTunes account, try authorising with the iTunes account you used.
Updating the iTunes software will not affect your existing iTunes account or music library.