Garang, head of the Sudan Peoples' Liberation Movement (SPLM), is due to arrive on Friday on his first Khartoum visit in more than 22 years to take up his post as first vice president a day later, in line with the accord.
Garang and his 200-strong delegation are to meet President Omar al-Beshir and a similar number of officials from the ruling National Congress Party (NCP) upon arrival, SPLM spokesman Yasser Arman told reporters in Khartoum.
After the meeting, the SPLM leader is expected to address a crowd of hundreds of thousands of people from north and south Sudan in the capital's main Green Square.
"It shall be the beginning of the process of normalizing relations," said Amal Abbas, a journalist and member of a National Reception Committee (NRC), headed by popular Sudanese singer Mohammed Wardi.
The NRC has organized a series of events in and around the capital to mark Garang's return to Khartoum, including musical performances, traditional dances and art exhibitions, and put up posters on the streets.
"He (Garang) will be received as a Sudanese and not a southern leader," Abbas stressed.
The SPLM signed an agreement with the government on January 9 ending more than two decades of north-south conflict that left an estimated two million people dead and four million displaced.
In Khartoum, Sudanese lawmakers approved all provisions of the constitution which, among other things, provides for a presidential republic with Beshir staying on as ruler, Garang becoming president of South Sudan and first vice president. He replaces Ali Osman Taha who will become second vice president.
The constitution was drafted by a commission that included a majority of NCP representatives and a little less than a third from the SPLM. The rest of seats were given to opposition figures.
In accordance with the peace deal, the constitution stipulates that general elections will be held four years into the interim period and that prospective contenders must first endorse the agreement.
Several southern militia commanders still have to sign on to the Comprehensive Peace Agreement and will not be represented in the interim institutions.
A new legislature is to be appointed shortly.
Until the polls take place, the NCP will have 52 percent of executive posts and legislative seats and the SPLM 28 percent.
Fourteen out of the remaining 20 percent will go to northern opposition parties, with the remaining six percent to be split among other southern groups.
Another key point of the deal is self-determination for the south at the end of the six-year interim period.
The constitution says that a law for undertaking the planned referendum should be issued in three years and that the vote should take place six months before the end of the transitional period -- in January 2011.
Nearly a dozen heads of state and governments, mostly from neighboring countries, have confirmed that they would attend Garang's swearing-in on Saturday.
The event will coincide with the lifting of the 16-year-old state of emergency in northern and southern Sudan and the release of political prisoners.
Sudan's two eastern states and three in the western Darfur region remain ravaged by ethnic minority rebellions against Beshir's Arab-dominated regime, with parts under rebel control.
Also on Wednesday, some 100 prisoners of war held by the SPLM's former armed wing -- the Sudan People's Liberation Army -- were released and flown to Khartoum from the main southern city of Juba, the International Committee of the Red Cross (ICRC) said.
The former POWs, who were brought to Khartoum on an ICRC-chartered plane, "were part of more than 300 POWs who are expected to arrive here this week," the organization said.