SUNDAY PM/MONDAY AM: It’s another big win for a family film after a dry spell filled with too many sci-fi movies. Twentieth Century Fox’s Night at the Museum 2: Battle Of The Smithsonian not only was the clear No. 1 at the North American box office this weekend, but also Ben Stiller’s biggest live-action opener ever. After opening to $15.3 million Friday, NATM2 received the family bump (+36%) for $20.6 million Saturday and $18.3 million Sunday to easily win the 3-day weekend with $53.5M. The pic finished the 4-day holiday with $70M, an impressive haul with so many half price kiddie tickets. Once again, Fox put together a massive global release: 4,095 theaters in North America, plus 8,100 runs in 93 territories internationally. IMAX showings generated $4.1M (8% of weekend) on 160 screens.

Museum 2 is the first all-audience comedy since Race To Witch Mountain way back in March, and Mall Cop: Paul Blart back in January. So the market was receptive to a pic that parents knew was safe for offspring. This reteaming of Ben Stiller and Owen Wilson and Robin Williams with director Shawn Levy, had to live up to the first in the franchise, which in 2007 opened at Christmastime and went on to earn $250.8M and worldwide $575M.

Museum 2 is likely to have summer legs, whereas Warner Bros’ Terminator: Salvation is already weak-kneed. The McG-directed 4th in the franchise starring Batman‘s Christian Bale is running out of steam after making $14.8 million in domestic grosses both Friday and Saturday and $12.7M Sunday for a 3-day weekend of just $43M from 3,530 venues. That’s much lower even than Watchmen‘s non-holiday opening. T4 finished with an underperforming $53.8M for the 4-day holiday, and $67.2M for the 5-day cume (including $3M from its Wednesday midnight showings and $13.5M from Thursday). Even though my box office gurus were confident Museum 2 would wind up #1, T4 “is pretty disappointing as most pundits thought it was going to win the weekend, as did most if not all of the tracking services,” a rival studio exec notes. Under and over age 25 males turned out, but the buzz turned rancid among fanboys who overwhelmingly didn’t like the pic. (Top critics didn’t either: there were only 33% positive reviews at Rotten Tomatoes). Warner Bros expected more, especially because T4 benefitted from worldwide awareness from that Christian Bale audio.

Sony is handling T4 internationally and releasing it in Asia next week but not until June for major overseas markets so as not to compete with its Angels & Demons. Domestically, that pic made $5.9M Friday and $8.3M Saturday and $7.7M Sunday, and will close in on $300M worldwide as soon as Tuesday ($286M now). It was battling for No. 3 with Paramount’s Star Trek and it was a close call: $21.8M vs $22.7M for the 3-day weekend, and $27.7M vs $29.4M for the 4-day holiday. Ron Howards’ pic has a $87.8M domestic cume while JJ Abrams’ reboot (which made $5.8M Friday and $8.7M Saturday and $8.5M Sunday) has a $191M North American cume starting its 3rd week. Rounding out the Top 5, Paramount’s spoof Dance Flick from the next generation of Wayans opened with a tepid $10.7M from 2,450 dates for the 3-day weekend, and $13.1M for the 4-day holiday.

FRIDAY 1PM: Latest estimates are that Warner Bros’ Terminator Salvation is tracking closer to Fast & Furious “but it’s going to take 5 days to get what they did in 3,” one rival studio exec notes. T4 opened with $13.5M Thursday including Wednesday’s $3M midnight shows and now looks to make $70M-$80M for the 5 days including Memorial Weekend vs Fast & Furious which did $70M in 3 days. Hollywood analysts are still insisting that Night At The Museum2: Battle Of The Smithsonian has the potential to open #1 with $80M for the 4-day holiday. But 20th Century Fox keeps insisting it’ll make $60M at most even if it does big business once the kids get out at noon today.

FRIDAY AM: Warner Bros’ Terminator Salvation chalked up domestic grosses of $13.3M from its Thursday opening, including $3M in midnight showings. The 4-day weekend estimates are now leveling out at perhaps $60M+ for this actioner and for 20th Century Fox’s Night At The Museum: Battle Of The Smithsonian.

THURSDAY 2:30PM: 20th Century Fox is saying they expect Night At The Museum: Battle Of The Smithsonian and Warner Bros’ Terminator: Salvation to be about neck-and-neck with $55M-$60M for the 4-day holiday. The studio even thinks Museum 2 could come in 2nd behind Terminator 4.  But rival studios and my own box office gurus think Museum 2 will be #1 with $85M by the end of the long weekend. We’ll see…

THURSDAY NOON: Get ready for a mammoth Memorial Day weekend at the domestic and foreign box office. But you knew that already. By Monday night, 20th Century Fox’s sequel Night At The Museum: Battle Of The Smithsonian should round up the family sample to end No. 1 with an estimated $85 million for the 4-day holiday.

Warner Bros’ Terminator: Salvation already brought in $3 million from its midnight showings and should end Sunday with an estimated $60M for the 4-day holiday and a $75 cume for the 5-day. It looks big with males under and over age 25 but “I wish them luck with female moviegoers,” snarks a rival studio exec. “There hasn’t been anything shown that should convince a female to go see the movie.” There’s also a lot of fanboy chatter since Harry Knowles’ review eviscerated T4 on his Ain’t It Cool News. The combo of Bale and director McG is new so hard to compare their pic with the franchise starring Arnold Schwarzenegger. But 1984’s T1 did $38.3M domestic and $78M worldwide, 1991’s T2 did $204.8M/$519M, and 2003’s T3 did $150.3M/$433M.

Studios expect Sony’s Angels & Demons after one week, and Paramount’s Star Trek reboot after two weeks, to be neck-and-neck for the weekend. Expect an estimated $25M apiece for the 4-day holiday. And, rounding out the Top 5 will be the Damien Wayans-directed spoof Dance Flick which features a genuinely funny trailer . Playing in 2,450 dates, it could finish the 4-day holiday with $15M.