Newb questions :)

Hey, I'm about to buy Guild wars and i have a few question.
Do i need all expension in order to play.If not which one do i need?
If i don't have for example the game Guild wars Nightfall can i still play with some one who have it?
It might sound wierd. I just want to inform myself before buying the game ^_^
Thanks.

The only one you cannot start with is Eye of the North; otherwise, you only need one of the other three - Prophecies, Factions, or Nightfall.

Are the other one upgrades to the game? will it change something if i buy them?
What would u recommend me?

Read For the new player on a budget: Which Guild Wars Should You Buy? and ask further questions there. Closed.