Carter on her scenes in The Deathly Hallows
In an interview to promote her movie Alice in Wonderland (also staring Johnny Depp), Helen talks a little on her role as the infamous Bellatrix LeStrange. Also, she's given us some insight as to where the break in scenes might be, the cut between part 1 & 2.
"The best bit about being Bellatrix in this one is also because I got to pretend to be Hermione," she added of a pivotal scene that has the evil witch's identity being assumed by Harry's friend in order to gain access to Gringotts Wizarding Bank, which holds Hufflepuff's cup — and a part of Voldemort's soul. "Because Hermione takes polyjuice potion and gets to look like Bellatrix."

After J.K. Rowling wrote the scene in the final "Potter" book, the film series' producers were faced with a difficult question: Was it preferable to use makeup and CGI to make Watson look like Bonham Carter, or have the older actress act like the younger?

"Rather than put Emma Watson in a helluva load of make-up they just said, 'Now you go act like Hermione,' " Bonham Carter said of their decision. "That was fun, because I always wanted to be Hermione."

"It was great fun," she said of the scene. "[I was] looking at Dan [Radcliffe] and Rupert [Grint] and they were treating me as if I was 17."
"I can't remember where they are going to cut," she explained, then remembered. "Yeah, [the scene is] definitely in the second one, because all of my stuff is in the second one. So you won't see me until 2011."

She also stated (after Hathaway asked), that the actors (she as well) got to choose their own wands. Said "It's a right of passage." And then laughed on about how they then keep all the wands under lock & key as if they really worked. Said no one's allowed off-set with one.
You can see her talking bout it on video HERE.

**There's also a piece (short and sweet) that Helen did for The Dishrag