NEW YORK — It’s about 8:30 p.m. on a brisk, Saturday evening in New York, and Nicole Richie is ready to party. Not the type of partying she did in the old days — which drew plenty of tabloid headlines — but the grown-up kind that comes with being the face of a bourgeoning fashion business.

Tonight Richie is the guest of honor at a small gathering hosted by Rick and Brian Cytrynbaum, co-founders of Modern Vintage and Majestic Mills and her fashion collaborators. They’re feting the spring ’10 launches of Richie’s House of Harlow footwear collection and Winter Kate apparel line.

Dressed in black platform House of Harlow booties, dark leggings and a long, silk Winter Kate cardigan with a colorful peacock-feather print, Richie strolls through the penthouse of the Cooper Square Hotel, taking in the 360-degree views of Manhattan and mingling with new fiancé Joel Madden, retailers and a cast of business associates.

The party marks the half-way point in a public-appearance blitz designed to promote Richie’s entry into the fashion world. It began last year with the launch of House of Harlow jewelry, and for spring ’10 has widened to include shoes and sunglasses, and apparel under the Winter Kate nameplate.

For the past two weeks, the former reality TV star and mother of two has been very visible in New York, where she appeared on “Late Show with David Letterman,” and has made international stops at department stores in Canada, Paris and London.

But before hitting the road last month, Footwear News visited the rising designer in Los Angeles, where things were a bit more quiet. At her studio in a tree-lined residential neighborhood near Beverly Hills, Richie is relaxed in jeans, a flowing Winter Kate sweater, chunky House of Harlow bangles and sky-high booties. She openly discussed her vision for the footwear collection and talked about plans for building the House of Harlow and Winter Kate lines — both named for her 2-year-old daughter, Harlow Winter Kate Madden — into a global lifestyle offering driven by her bohemian-chic style.

“I would like for it to be the best version of itself,” Richie said at the studio, where she pores over magazine clippings, colorful fabrics and art books to find design direction. “This is the first time people are going to see my clothes, footwear and sunglasses, [and] I’d really love [for it] to be the biggest and best it can be.”

While Richie isn’t making any bold predictions going into her footwear and clothing launch season, Rick Cytrynbaum, who, along with brother Brian, is producing those collections, is confident he’s got a winner.

“The success has been so tremendous,” he said, noting that the footwear line — priced between $150 for flats and $395 for boots — is launching in 23 countries, including the U.S., Japan, Russia, France, the U.K., Australia and Canada. “We’re also in talks with retailers in the Middle East and all over the world to grow the brands and are focusing on each market independently.”

House of Harlow, Cytrynbaum said, also will expand the sunglasses offering and launch handbags, and a higher-end footwear collection is set to debut under the Winter Kate label. Branded retail wouldn’t be far behind, he added, with a potential U.S. store opening in 2011.

“This will definitely be a lifestyle brand, [but] we need to get it right before we can move on to the next category,” he said, predicting that the footwear component could bring in several million dollars in sales in its first year. “We’re not going to rush it because it’s important that everything matches Nicole’s vision. There has to be that authenticity, that integrity.”

Retailers agreed that Richie’s stamp on the line brings credibility in a saturated celebrity market.

“People have a huge obsession with her and what she wears,” said Jon Singer, owner of Great Neck, N.Y.-based store and e-tailer Singer 22. He said he’s picked up about 90 percent of the line and already carries the jewelry. “We have been pre-selling a ton, [and] I know it’s going to blow out. We’re not going to have enough, and that’s not a bad problem,” he said.