Why is Willy interested when Biff mentions Bill Oliver? Why do they argue? How does Happy try to capture attention?

1) Willy thinks that Bill Oliver can fund Biff's proposed sporting goods store, and give his some a chance at a career and some direction in his life.

2) Biff and Happy are talking with Linda about Willy. Biff and Happy learn that Willy is on straight commission and has been borrowing money from Charley in order to pay bills. Linda criticizes her sons for abandoning their father in order to pursue their own selfish desires, and she gives Biff a choice: Respect your father or do not come home. Biff decides to stay in New York, but he reminds Linda that Willy threw him out of the house. He also tells Linda that Willy is a "fake." It is at this point that Linda informs her sons that Willy is suicidal; Willy overhears his wife and sons talking, and he and Biff argue.

http://www.cliffsnotes.com/study_guide/literature/death-of-a-salesman.html

3) Happy describes Biff's plan to open his own business