New York ? The downside to being famous is that everything is borrowed.

That’s the inside track on celebrity from Karen Robinovitz and Melissa de la Cruz, two formerly unknown fashion writers who turned themselves into boldface names. They’ve made it onto several “A-lists” including the one jeweler Harry Winston uses to gauge who is worthy of borrowing baubles. The women wore $4 million in diamonds to the launch party for their book “How To Become Famous in Two Weeks or Less” (Ballantine Books).

The jewels added sparkle to the already glitzy event that attracted model Molly Sims and actor Evan Handler.

Robinovitz wore an on-loan Gucci dress adorned with white feathers, and de la Cruz covered her back with the same $8,000 kimono that Liv Tyler wore to “The Lord of the Rings: The Two Towers” premiere.

But neither the jewelry nor the fancy clothes are still in the women’s closets.

“I hate when that messenger comes to my door the next day to pick everything up,” says Robinovitz.

However, she adds, being a celebrity is worth it, no matter how fleeting one’s time in the limelight.

“Fame is a public way to show you’ve made it,” agrees de la Cruz. “And since everyone is still trying to get over high school, especially when you were the outsider who stayed home on Friday nights watching ‘Quantum Leap,’ being famous is good payback.”

Robinovitz adds: “Being famous gives you the feeling of always being picked first on the team, and who didn’t dream of that?”

De la Cruz and Robinovitz share tips in their book on how everyone (and this means you, they insist) can become a star. They say that while fame is measured differently depending on personal standards — to some, getting a table at a trendy restaurant means you’ve made it; for others, it’s getting the paparazzi to chase you down the street — the method is the same.

Aspiring celebrities have to see themselves as a brand and market themselves accordingly; you’re nothing if you don’t have a press kit and a trademark look, de la Cruz and Robinovitz advise.

But doesn’t a young woman have to be thin, beautiful and talented to win fame and fortune?

Absolutely not — look at Madonna, the master of keeping herself as one of the top “It girls.”

“Madonna was one of the first celebrity ‘brands.’ She’s not the most beautiful or the most talented, but she makes you think she is,” Robinovitz says.

Madonna also limits herself to a few public events each year, both keeping her in the public eye but also keeping some level of mystique.

Robinovitz notes, though, that there is a fairly clear line between celebrities who just look good on a red carpet and the Oscar-caliber-yet-beautiful actresses the other starlets are trying to emulate. One group doesn’t risk canceling out the other thanks to an endless string of entertainment magazines and Web sites.