Oh Yes It Is!
It's not a dual-boot. Check
here.
Sorry, even though Window expert, Scot Finnie, indeed talks about running Window's via VMWare or Parallels Desktop for Mac, Apple, itself, also provides a beta program for duel booting, called BOOT CAMP, which will be a standard feature in the up-coming release of the 64-bit, Hyper-Treaded, Leopard OS.
As a Mac user for the past ten-million years, eight-months, four-weeks, 5 days, six-hours, ten-minutes and thirty-five seconds, I can assure you it is a very real dual booting system. The only let down is that you have to reboot from OSX and vice-versa, which is not necessary when using Parallels or VMWare.
VMWare provides gaming support, Parallel doesn't, but promises to in the near future.
http://www.apple.com/macosx/bootcamp/