You mean HDV, not HD right? For HD, I reckon we'd be talking some really really serious hardware. But the HC1 is an HDV camera, so you'll be fine with either of the above.
Having said that, I'm with iSlayer on this - I've edited HDV on an iBook and an iMac G5, and while they're sufficient, they are far from ideal - slow render times and lack of real time filters is a big downer. But editing HDV on at least a dual 2.0GHz Powermac G5 with as much RAM as you can put in (but at least 1GB) is a dream, just as easy and efficient as editing DV on lesser hardware.
By the way, great camera! I've seen great things from the HC1 - I've got an FX1, and I'd love to see how the HC1's CMOS imaging compares in actual use to the FX1's CCDs.
[EDIT] By the way, I'd treat any rumours of updated Powermac G5s at the moment with some skepticism - there's nothing solid out there, and you shouldn't delay your purchase for speculated updates, particularly when they're not fairly solidly supported at the moment.