If you want to get the latest content for whatever reason, which contains all the chapters, then yes, get Nightfall, FIRST.
Then buy the others with whatever means there are, online from plaync, instore from ingame or from a shop shelf.
Same difference really, it all just depends how much you wanna spend and how long you wanna wait.
All the online versions are more expensive (euros vs dollars vs rand

) than what you get in a store or buy locally.
An
online STANDARD edition can easily cost the same as a
local COLLECTOR's edition.
Hopefully you will get enough time to play Nightfall and then go back and experience Factions and Prophecies in all their splendour
You create a master login on
www.plaync.com. This account is what you will use to login to Guild Wars with and your password. On this master account login screen (first screen after launching Guild Wars) you can add as many access keys you want, but only one per Guild Wars chapter. For instance, a Factions standard key will overwrite a previously added Factions Collector's edition key.
Adding the keys in this manner ensures you can travel between the 3 different continents.
BTW, you don't have to do the master account creation online (through the plaync website), you will get prompted when the game installs from a CD/DVD, if you bought a local version (not online). In fact, just downloading the gwsetup file (from Guild Wars website for instance @
http://www.guildwars.com/support/downloadclient/), will ask this as well.
Choices are yours to be made.
