Although the results show only a slight nod to Mac OS X compared with Vista (which is surprising), the performance results are no less than astonishing. As Popular Mechanics says,

In our speed trials... Leopard OS trounced Vista in all-important tasks such as boot-up, shutdown and program-launch times. We even tested Vista on the Macs using Apple’s platform-switching Boot Camp software—and found that both Apple computers ran Vista faster than our PCs did.

One really interesting fact here is that the test iMac had only 1GB of RAM, whereas the PC had 3GB. The iMac did have a 2.4Ghz processor, compared with 2.0Ghz for the PC, but the difference in performance is still impressive considering the huge difference in RAM. Just proves what a RAM hog Vista is. Yet, Vista still ran faster on the iMac with 1/3 the RAM... like I said, impressive!

Oh, and it's also worth noting that despite very similar specs, the iMac is $300 less than the Gateway.