Gavin Andresen - 2011-03-23 21:14:20


No.  The end of the chain can, and does, fork, but the forks are short and the network pretty quickly decides on the One True Chain.

Yes.
Short answer: no.

Longer answer:  it is complicated, and what you need depends on whether or not you're trying to generate new blocks.  To keep it simple, the original client downloads everything.