Ashlee Simpson's doing double duty for her appearance on "Saturday Night Live" this weekend -- not only is the singer going to perform her new single, "Autobiography," but she's also going to participate in three of the show's skits. In one of those, she'll spoof a notorious party girl.

"I'm going to play Tara Reid," Simpson said. "I have to watch a video on it, because I don't really know how to act like her, but it will be really exciting to do it, to be part of the whole sketch thing."

In another skit, Simpson will riff on how she's constantly being mistaken for her famous older sister, Jessica.

Despite her extra acting duties, as far as pulling off the show goes, Ashlee said that she feels really "comfortable and confident" -- well, confident about everything except working with the guest host, Jude Law.

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[article id="1492960"]Click for photos from Ashlee Simpson's "SNL" rehearsal[/article]

"I just finished doing the promos with Jude Law, and I was completely nervous the whole time because he was so hot," she said. "I didn't really touch his butt. I thought about it, but I didn't do it."

Most of all, Simpson said, she's just really excited to be doing the show after watching it for so many years. "It's just really cool, just even to be on the set. I can't wait."

Simpson's episode of "Saturday Night Live" airs Saturday on NBC at 11:30 p.m. ET.