Quoting CNET
With VMware's official release of Fusion 1.0 less than two weeks ago, there are now no less than four different ways to run Windows applications on Intel-based Macs. Fusion, as well as SWsoft's Parallels Desktop 3.0 for Mac use virtualization technology to allow you to simultaneously run the Windows operating system as a virtual machine alongside the Mac OS. CrossOver Mac 6.0 from CodeWeavers uses a different virtualization approach by building on the open-source API, Wine, which allows you to run individual Windows applications in the Mac OS without needing to install or run the Windows operating system.
Perhaps the easiest and most common way to run Windows on a Mac today is with Apple's own Boot Camp Public Beta. While Boot Camp is currently the only way to run Windows natively on a Mac, it requires booting directly into the Windows OS, during which the Mac OS is not accessible (until you reboot the computer back into the Mac OS, leaving the Windows OS).
With all these different options for running Windows applications on Intel Macs, we wanted to see how they compare against each other in terms of performance; so CNET Labs applied its systems testing methodology to an eight-core, 2.66GHz Mac Pro running the Mac OS X 10.4.10. We used Boot Camp 1.3 Beta, CrossOver Mac 6.1.0, Parallels Desktop 3.0 for Mac (4560), and Fusion 1.0 (51348). Windows Vista Ultimate was used as the operating system for Boot Camp, Fusion, and Parallels. Fusion and Parallels were both set to 1,024MB of system memory, a 32GB hard disk, and the maximum amount of graphics memory they each supported (Fusion: 128MB, Parallels: 64MB).
Multimedia multitasking test (in seconds)(Shorter bars indicate better performance)
Apple Mac OS X 10.4.10
248
Apple Boot Camp 1.3 Beta
529
Parallels Desktop 3.0 for Mac
3,260
Note: Apple QuickTime 7.2 and Apple iTunes 7.3.2.6
Read the rest of the Lab results, here.