I wish I could say that there's still hope for the scene, but there's not. Really. Shame on ... well, whoever you think.
Ok, I try to keep it as short as possible, but this is always a problem when you try to explain Tolkien
Ok, now: as we knew from TTT, Merry and Pippin landed in Isengart, along with a whole bunch of Ents. No, I have to start even earlier:
Gandalf, who wandered as Gandalf The White through Fangorn, had a few talks with Treebeard and knew that the Ents were going to flood Isengart (a scene that explain this will appear on the extended version of TTT).
After the battle for Helm's Deep, Gandalf, along with Theoden, Eomer, Aragorn, Legolas, Gimli and a couple of Rohirrim rides to Isengart, now here it comes, >with the intention to meet Saruman<.
After gandalf's "death", he was sent back as The White Wizard, the head of the White Council (don't know the English term for it, sorry), the "chief wizard" if you want.
Before Saruman's treachery, HE was the White Wizard and Gandalf was the Grey Wizard, one level below.
And now, it is Gandalf's JOB to "fire" Saruman. He talks to him and offers him to hand over his "magic wand" and the Key for Orthanc peacefully. Of course he refuses and Gandalf breaks his little magic stick.
Wormtongue, who is still at Saruman's side, tries to protect his master and tries to kill Gandalf by throwing the Palantir out of the window of Orthanc (Grima doesn't know the power and meaning of the stone).
You know, the thing Saruman uses to communicate with Sauron.
He missed him and the Palantir lands in the mud.
OK; until this point, the movie would most likely have followed the story of the book.
Now, in the book, after this Palantir-thing, Pippin picks it up and wants to look at it, but Gandalf rips it out of his hands and keeps it safe under his coat. As they walk away, they hear a scream from Grima. I suppose Saruman tortured him a bit for throwing the Palantir away.
In the movie, following would have happened:
Grima would have throwed the stone away, and Saruman, in rage, shouts that Grima killed Theoden's son by pouring poisen into his meal, adding the sentence "And you always do what you're told, don't you, worm?" or something like this.
Grima, enraged, grabs a knife, cuts Saruman's throat and kicks him over the balcony of Orthanc onto a spiked wheel. Then, Legolas grabs an arrow and shoots Grima.
Now, this is only the scene. But the consequences are important:
after this event, Pippin develops a strange affection to the Palantir and once at night, he steals it from Gandalf and looks into it. Sauron sees Pippin, thinking he's the Halfling with the ring, captured in Isengart (you know from FOTR that Uruk-Hai were sent out to look for "two halflings"). Sauron sends a winged Nazgul to Isengart to look how things are going. The Nazgul discovers the devastated Isengart, brings this news to Sauron, who, obviously in panic, sends his army earlier than planned to Minas Tirith, which is a factor why the city won't fall later on (oops, spoiler...).
However, Pippin screams after he faced the pure evil and Gandalf takes care of him. He begins to understand that Sauron believes now that Pippin is the ringbearer and rides with him to Minas Tirith because that is the safest place at that time in Middle-Earth. He also has in mind that Pippin can tell Denethor, stewart of Gondor, about his dead son Boromir.
Gandalf hands the Palantir to Aragorn, who is the rightful owner of it (due to the line of kings or whatever; don't ask me about THIS

).
He also looks into the stone and after a long mental fight, he is able to regain the power over the stone. Remember one scene from the first teaser of ROTK, where Aragorn says "He remained unchallenged long enough" ?
The fact that Aragorn, Isildur's heir, the heir of the one man who destroyed Sauron once, reveals himself to Sauron, drives him into even more panic.
The consequence is that Sauron focuses his eye even more on the other lands instead of his own, which gives Frodo a higher chance.
A bit compicated, isn't it?
Hope this helps.