With that machine? You could probably run it on VMware fusion with no lag.
Run it on mac, you'll never see any difference.
Yup, Blizzard is the single best dual-platform developer, and has been for years. Combine that with their hybrid installation media, and they've got a big fan from me, and I don't even play WoW anymore!
Go with the OSX install.
WoW originally came out about 5 years ago right? Since today's intel macs are about 10x the speed of the g4s that ran it ok 5 years ago, you could run it on an intel mac in windowed mode with lots of other stuff going on and you'll be fine.
Well it's not that simple. Wow's graphics engine went through tons of changes since the launch so it's much more demanding nowadays which actually cripple the fastest pc's.
I know, it's almost too good to be true
There are some issues with mac wow, though. For example, my expose keybindings had a 50% chance of being gone after playing wow, and you can't use the CMD-key in keybindings in wow.
Of course, this was a year or two ago when I played.
Yeah, it's so demanding that tens of millions of people have the fastest PC's to play it on. Blizzard made sure that it's highly scalable, and even at the highest settings it's relatively easy on the GPU. Some guy posted a video on his 27" C2D iMac, at max settings at native resolution and runs at 60 fps in most areas.
I quit playing about a month ago. My mac is a MBP with an x1600, obviously your video card is much faster, but this is what I noticed:
On Windows, WoW runs much smoother, and starts up faster. My mbp also runs cooler when playing WoW in Windows. But also, the Windows mouse drivers weren't as refined as they are in OS X, so Apple, by way of crappy Windows drivers, forced me to play in OS X whenever I didn't have an external mouse lying around. It runs OK in OS X, but it was definitely optimized for Windows.
I can't freaking WAIT for Diablo 3. Someone calm me down.