Gidzenko boarded the outpost first, returning to a larger station than when he served as a member of the Expedition One crew more than a year ago.

Floating in behind Gidzenko was European Space Agency astronaut Roberto Vittori, who is part of this taxi mission under a deal struck between the Italian Space Agency and Rosaviokosmos -- the Russian Aviation and Space Agency.

Last onboard was Shuttleworth, the 28-year-old Internet entrepreneur from South Africa who is the second fare-paying passenger to be allowed onboard the multinational outpost.

Having spent the past two days inside the cramped Soyuz spacecraft since Thursday's launch from the Baikonur Cosmodrome, the three men wore smiles as they entered the more spacious modules of the space station and could be seen moving cautiously and deliberately as they found their space legs.

All six humans now in space then gathered briefly for a welcome ceremony and received greetings from Russian, Italian and European Space Agency officials. A call to Shuttleworth from the South African President Thabo Mbeki came later in the day.

"It's amazingly roomy,'' Shuttleworth told the president. "Although it's very, very large, we have to move very carefully. As you can see around us, there are tons of very precious and very sophisticated equipment. We hope that we will be good guests"

As for his liftoff two days earlier from Kazakhstan, "I had moments of terror, moments of sheer upliftment and exhilaration,'' Shuttleworth said. "I have truly never seen anything as beautiful as the Earth from space. I can't imagine anything that could surpass that."

The world's latest space tourist -- dubbed an Afronaut back home -- has generated huge excitement in South Africa.

"The whole continent is proud that, at last, we have one of our own people from Africa up in space,'' said Mbeki, taking part in celebrations for Freedom Day, marking the 1994 elections that ended Apartheid. "It's a proud Freedom Day because of what you've done.''

Shuttleworth's parents were relieved to see their adventure-seeking son, an entrepreneur who made his fortune off the Internet, safely aboard space station Alpha. They watched from Russian Mission Control outside Moscow as the Soyuz capsule smoothly docked with the space station.

"It was one of the dangerous procedures and my stomach was in a real knot before it started. But I'm feeling much better now,'' said his mother, Ronelle Shuttleworth.

For the Expedition Four crew, who just said farewell to the crew of shuttle Atlantis a little more than one week ago, the three new humans were a welcome sight.

"We're very happy to have another group of visitors onboard and it's always great to see new faces," Walz said.

With the formalities out of the way the combined crew set out to shut down the new Soyuz's systems, exchange "seat liners" between the old and new Soyuz spacecraft and run through a safety briefing.

The seat liners are what Soyuz crewmembers sit in and are form-fitted to each person, so the custom liners for Gidzenko, Vittori and Shutleworth must be removed from the Soyuz TM-34 vehicle and installed in the old Soyuz TM-33 vehicle that is attached to the Pirs docking port. At the same time, the liners for Onufrienko, Walz and Bursch must be removed from the TM-33 spacecraft and installed in the TM-34 ship.

The shuffle is a confusing but necessary task that is part of space station operations.

At least one three-seat Soyuz spacecraft remains docked to the station at all times to serve as an emergency escape pod, but it must be replaced every six months to ensure that all spacecraft systems remain in good working order.

The Soyuz TM-34 delivered today is the fourth Soyuz to see duty at the outpost since the Expedition One crew first arrived at the station in November 2000.

The job of taxiing up a new Soyuz and returning the old one to Earth requires a crew of at least two people.

As a result, Rosaviokosmos has been marketing the third seat to raise additional money for their programs with the help of firms such as Arlington, Va.-based Space Adventures, Ltd.

American businessman Dennis Tito claimed the first seat in April 2001, paying a reported $20 million for the honor of becoming the world's first space tourist. The next available seat last Fall went to a professional astronaut from the European Space Agency.

And for this Soyuz flight it's Shuttleworth, who paid the fare and was allowed onboard after passing medical tests and completing several months of training in Russia and the United States.

One of the youngest persons ever to fly in space, Shuttleworth has repeatedly expressed disgust over being called a tourist, highlighting the fact he has invested additional dollars to shape his own space science and education program.

"I'm trying very hard to do serious work up there," Shuttleworth told SPACE.com during a pre-flight interview. "My greatest concern is being in a position to do good work and not be a burden on the space station crew."

For the next week he'll have his chance to prove himself before Shuttleworth and his crewmates must say good bye, board the Soyuz TM-33 and return to Earth. Undocking is scheduled for 8:20 p.m. EDT next Saturday (0020 Sunday GMT).

The Associated Press contributed to this story.