$77M is not good for a film that needs to make back $300M+ in production costs. The latest Transformers movie made $200M in it's first long weekend (It started on a Wednesday, made $91M thru Thurs, then another $109M on the regular weekend).
Movies generally make about half of all the gate-money they will ever make in the first two weeks of release, and only half the gate goes to the studio in the first two weeks, decreasing thereafter.
It will probably break even with foreign sales plus DVD, but the first weekend turnout will probably seem disappointing to the studio.
In addition, from revised article: Fox is also on the hook for worldwide marketing costs of $150 million, and must share some profits with Cameron. DVD sales will add to the windfall, although critics say "Avatar" is best appreciated in a 3-D theater environment.
Cameron is going to make out like a bandit on this. He will definitely beat Oliver Stone for The 2009 MP Academy Special Leni Riefenstahl Award ("Oscar"). Oliver will come back next year with Wall Street 2.