You can get the main campaigns for GW now for a mere £20 from most retailers, play occasionally has them for £15 each.
Prophecies and Nightfall are the best main campaigns and Eye of the North is a true expansion requiring one of the main campaigns to be able to play it.
If you head over to the PlayNC site you can get the client there but it is a big download. I believe you can get it from FilePlanet also.
http://www.fileplanet.com/182347/180...Trilogy-Client
Or for people interested in GW :
http://www.play.com/Games/PC/6-/Sear...searchsource=1