Von neumann vs Harvard architectures

[shekhar_dandya]

HI All,
What is the difference between Von neumann architecture & harvard architecture?
Is it that von neumann has unique address space where all the instructions,data & peripherals are mapped whereas,harvard has seperate address spaces for instructions & (data + peripherals).WHat about the address & data busses?
Is it that von neumann has only one address and data bus whereas harvard has 2 address& 2 data busses?
please clarify my confusion.
-Shekhar