Hi,
I have a dual 2.0GHz G5 and a 1.5Ghz Powerbook, and I run Nuendo 3 and Pro Tools LE on both... we also have a monster PC at our studio, and one of those crazy fast gateway laptops. So I guess you could say I've had well-rounded experience using Nuendo 3 on both Mac and PC. Here are some considerations for you:
-Nuendo 3 (2, as well) runs MUCH smoother overall on PC. All across the board... editing, zooming, everything... it's way faster. The G5 runs Nuendo pretty well... but it's still not as fast as even the gateway laptop.
-There is NO direct monitoring in Nuendo on a Mac with OSX. (with OS9 there WAS direct monitoring). This is a HUGE consideration... it's what made us switch to PCs at our studio.
-That being said: Windows crashes, PCs suck with firewire drives, they aren't as stable as Macs, and definitely not as cool. I'd stick with Mac if direct monitoring is not an issue for you (i.e. if you have a traditional console or some other way of sending cue mixes before your software).
my 2 cents
-Aaron