U.S. astronauts Kenneth Bowersox and Donald Pettit and Russian cosmonaut Nikolai Budarin welcomed American Edward Lu and Russian Yuri Malenchenko aboard the space station after their Soyuz TMA-2 capsule docked.
The crew is showing show Lu and Malenchenko around the station - much changed since the two were there in 2000 - and update their own knowledge of the Russian Soyuz, which they will use to return to Earth on Saturday.
Originally, they were to return in the Atlantis, but the U.S. shuttle fleet has been grounded since the Columbia disintegrated during re-entry on Feb. 1, killing all seven people aboard.
At Mission Control outside Moscow, relatives and flight controllers applauded when the Soyuz docked with the station, about 250 miles above the Earth.
"I am just so happy and proud to see everything work out so well," said Lu's mother, Snowlily.
His fiancee, Christine Romero, also was among those watching the docking.
"Everyone is proud - not just for what Ed is doing, but for NASA and the international space station and for the space program as a whole, especially after the Columbia," she said.
All five men crowded together for a videolink with Mission Control. They grinned as NASA and Russian space officials congratulated them.
"We're very, very proud today at the work of our international team," Bowersox said.
Malenchenko said the outpost has grown since he was there.
"It has become so big and beautiful," he said. "We are very glad to be here, very glad to see our friends."
He and Lu blasted off Saturday from Russia's Baikonur cosmodrome in Kazakhstan on their way to the $60 billion station.
Frederick Gregory, deputy administrator of NASA, said the international space station partnership has demonstrated its ability to overcome "any obstacle on this road to the future."
As the investigation into the Columbia disaster continues, it is not clear when shuttle flights will resume.
The Russian Soyuz became the only ship capable of carrying crews to and from the space outpost, giving it a vital role in keeping the station manned. The Soyuz trip was put together in record time.
Maintaining a manned presence on the space station and keeping it in good condition is vital until shuttle flights resume, at which point work on building and developing the station can continue, Gregory said.
Saturday's flight to Earth will be the first time U.S. astronauts have returned in a Soyuz. Bowersox, Pettit and Budarin are familiar with the technology, since a Soyuz is always kept at the station as a lifeboat.
The three returning crew members will be taking back an older Soyuz already docked at the station, while the one that carried Lu and Malenchenko will stay there in case they need to quickly evacuate. The two are to remain at the station until October.
The crews will also try to fit some birthday celebrations into the five days they're spending together. Pettit turned 48 on April 20, and Budarin turns 50 on Tuesday. Lu and Malenchenko brought gifts.