I've just picked up someone's playset of "everything up to and including the Legends box" what sets does this cover? What packs will I need to get to turn this into a complete playset of everything so far?

http://www.fantasyflightgames.com/edge_minisite_sec.asp?eidm=85&esem=2

http://www.cardgamedb.com/index.php/warhammer/warhammer-invasion-card-spoilers

Those links should help you inventory what you have.