why does Israel think that the U.N. be able to do what it won't, disarm Hezbollah?

Answer 1

Because president Ehud Olmert is a stupid man (and a hack politician). He's hoping for a "free lunch" But if will not happen. The I.D.F. will have to clean Hizbullah out of its bunker trenches and tunnels. Just the U.S. marines did in Okinawa, and Iwo Jima. It is dangerous, expensive work but that cancer must be cut out and to Hell with world opinion that bleeds over innocent Lebanese victims and cares not at all for Israeli civilians.
D.

Answer 2

looks to me like they're challenging the UN to the task since the UN criticizes every little thing israel does.