Reading out the communique, Tomaz Salomao, head of the regional bloc, said that the summit decided that "the inclusive government be formed forthwith in Zimbabwe" and "the Ministry of Home Affairs be co-managed between the ZANU-PF and MDC-T."
Zimbabwean President Robert Mugabe and opposition leader Morgan Tsvangirai signed a power-sharing agreement in September, but the deal has hit the rocks over the disputes about control of the most important cabinet posts.
Both the opposition Movement for Democratic Change (MDC) and Mugabe's ZANU-PF want control of the powerful home affairs ministry.
South African President Kgalema Motlanthe, whose country holds the rotating SADC chair, had earlier said it was disappointing that it had been two months since the signing of the agreement and the parties have not yet been able to conclude the discussions on the formation of an inclusive government.
Motlanthe urged the political leadership in Zimbabwe to show political maturity and put the interest of Zimbabwe first.
However, Tsvangirai warned that the deal appeared to be slipping away.
"In practical terms, you have two ministers, one appointed by ZANU-PF, one by MDC," he said.
SADC nations are prepared to provide assistance to the DRC and send peacekeepers if needed.
The SADC decided that "the security situation in the DRC is affecting peace and stability in the SADC and the Great Lakes regions."
"The security and humanitarian situation is deteriorating in the eastern part of the Democratic Republic of Congo," the communique added.
"SADC should immediately provide assistance to the armed forces of the DRC," Salomao said.
The SADC would not stand by and witness incessant and destructive acts of violence by any armed groups against innocent people of DRC, if and when necessary, SADC will, within the Nairobi framework, send peace peacekeeping force into Kivu Province of the DRC, he added.
According to Salomao, the DRC armed forces need to be assisted to protect the country's territorial integrity and sovereignty.
The SADC Military Monitoring Commission would be dispatched to the DRC immediately to monitor the border between DRC, Burundi, Rwanda and Uganda, he said.
The region would also ask the United Nations to expand the mandate of its peacekeeping mission, known as MONUC, which is not allowed to engage in active clashes in eastern DR Congo.
Salomao denied reports that Angola had already deployed troops inside the DR Congo, but said they could be sent in quickly if needed.
The summit decided to have a SADC representative in the mediation mechanism established by the Great Lakes Region for the DRC to be based in Nairobi, Kenya, with immediate effect, he said.
According to the United Nations and humanitarian aid groups, the latest round of fighting in eastern DR Congo had displaced more than 250,000 civilians and killed at least 100 since September.