The squatters want a deal. You help them become self sufficient and they'll give you access to the vault.”— Chosen One to President Tandi
Complete Deal with NCR is a quest in Fallout 2.
As a formality, this quest only requires that you talk to President Tandi, informing her that the squatters at Vault 15 will cooperate with the NCR, and accept their presence. The end results being, Zeke gets a spiffy new house, the squatters get a life (food and water), and the NCR launches its expansion campaign in Northern California.
This is also the penultimate step in the overarching Retrieve Parts/Gain Access to Vault 15 quest.
After completing this quest, Zeke will ironically say that he hasn't got enough food to survive, even if the NCR helps the squatters.