by Marilyn Beck and Erick Johnson We're all familiar with the phrase, "Two is better than one." After all, what lottery playing adult wouldn't want his or her lucky number to come up twice in a lifetime? And as we all know, the double scoop of ice cream is very popular amongst the juvenile set. However, when it comes to being successful in Hollywood, does being a twin help or hinder one's career?

Of course, the first and most obvious example on the side of the affirmative is the multi-million-dollar corporation known as Mary-Kate and Ashley Olsen. At only 17 years old, these showbiz tycoons have already found themselves in the company of the likes Oprah Winfrey and No. 1 box office draw Julia Roberts, when they made Premiere Magazine's annual list of Hollywood's 100 Most Influential Women. The Olsen's company, Dualstar Entertainment Group, in which they're partnered with Robert Thorne, licenses a line of Mary-Kate and Ashley girls' clothing and accessories, design of which the girls oversee themselves, to Wal-Mart -- as well as producing books, electronics, games, dolls and straight-to-video movies. This is in addition to the money they've made as actresses, in features and on the long-running "Full House." They started the series at 9 months, and made $150,000 per episode -- each -- by the time it ended when they were 8.

Another success story is that of Tia and Tamera Mowry. The now 24 year-old actresses were able to capitalize on their "twinness," as well as comedic acting ability, with their sitcom "Sister, Sister," which ran from 1994-99. Though both are currently finishing their last year of a psychology degree at Malibu, California's Pepperdine University, they're looking to defer the use of their psych degrees to do more in entertainment.

Declares Tia about what their fans can expect in the near future, "We're working with some producers, recording songs that are a mix of R&B, hip-hop and pop. We sang and danced long before we ever acted and we're really excited about the album we're working on for Columbia."

No release date for the CD has been set, but the Mowry's expect it to hit record store shelves by year's end.

While Mary-Kate and Ashley and Tia and Tamera have found success as showbiz twins, there are many that have found partnering with one's twin a more challenging aspect when it comes to entertaining.

For example, 30-year-old twin brothers Jeremy and Jason London have found that being a twin can often times be limiting as an actor. The brothers have auditioned for the same part on more than one occasion and for that reason each has seemingly narrowed his focus in the last few years.

Former "Party of Five" co-star Jeremy has become a series regular on the WB's "7th Heaven" -- and his brother Jason is focusing his attention on doing big screen work like the upcoming action/comedy "Grind" from Warner Bros., due to hit theaters in August. He also has in the can the indie comedy "Wasabi, Tuna" and is set to star in Dimension's 2004 release "Dracula III: Legacy." So now as Jeremy is concentrating more on television and Jason on features, the two won't likely be up for the same parts as they were earlier in their careers.

Many of yesteryear's twin acts haven't really had much staying power. Take singers Matthew and Gunnar Nelson for instance. They had a couple of hits in the early '90s but not much since.

And does anybody remember the pin-up Barbie twins? After making the B-List talk show circuit rounds in the mid-to-late '90s, not much is made of the one-time calendar sensations.

The jury's still out on twin pop stars Evan and Jaron Lowenstein. Their careers seemed to take off like a rocket once the two self-taught guitarists made legendary Jimmy Buffet a big fan. A record deal soon followed. And after that were a couple of top 10 hits, as well as CD and tour. But what's next?

Their next CD will have to be as good as the last one to prove to lots of critics they're not just a singing Doublemint ad.

And then, believe it or not, there are many twins of famous actors and celebrities who have shunned the spotlight altogether. Isabella Rossellini's twin sister Isotta become a professor of Italian Renaissance literature at New York's Columbia University, instead of an actress like her twin or their mother, the late Ingrid Bergman.

Vin Diesel's twin brother, Paul Vincent, (Vin's real name is Mark Vincent), has chosen a career behind the camera as an editor.

And who knew Iowa born model-turned-actor Ashton Kutcher had a twin brother named Michael?