I would bet on it.
I think Leopard is supposed to run natively on both flavors of Mac.I never upgraded to Tiger, and since I don't do anything more challenging on this Mac than a trivial spreadsheet, I don't actually need a shiny new computer or even a new OS. But I think at some point ya hafta find out what the noise is about . . .
Off topic a bit, Walter Mossberg's advice column in the WSJ today quotes Steve Jobs to the effect that the iPhone will not be capable of accepting third-party software out of the box on June 29 - but that "that is our intent," and he expects it to happen by the end of the year.
YEs it will. File system support is a factor of the OS, not of the hardware itself.
With existing machines, you will have to repartition and reformat your hard disks.