We will be travelling primarily in Greece and Italy. Does anyone have any thoughts as to the best and cheapest ways to get around within these countries? In short, what I am looking for is:
—Is it cheaper to buy regional/country/point-to-point rail passes here in the US or buy them when we get there?
—Assuming we will be travelling on alot of ferries in Greece, would the above question still apply and/or can you buy a ferry pass?
—Busses within Italy?
—Car rentals?

Our general 3 month plan is as follows:

Fly into Athens; do a little of interior Greece ( 1 week); Greek Islands ( 3 weeks); Tunisia ( 1 week); Sicily ( 1 week); work north through Italy (@ 4 weeks); maybe a side trip to Croatia and Slovenia for a week or two.

Thanks for the help!