If you're anxious about switching from a PC to a Mac, consider this: There are a multitude of ways you can virtualize Windows within OS X, and they all work uniquely well. Here's how to choose the right one.
There are three major virtualization products for Mac, and at their core, they're all quite similar. Each creates a virtual machine, which is to say, crudely, a software implementation of a separate computer. When you install Windows in a virtual machine, Windows thinks it's installed on a PC with a somewhat generic set of hardware. In fact, the hardware it thinks it's installed on is a software construct, and any time Windows utilizes what it thinks is a hardware component, its requests are actually being passed through to your Mac's real hardware.
Anyway! What's going on under the hood is conceptually similar among the most popular virtualization apps, but the ways they install, run and integrate Windows inside of OS X vary wildly. So, assuming you're ready to take the virtualization dive, which app should you use? VMWare Fusion 3? Parallels 5? Sun VirtualBox? They're all different, but in a strange way, they've ended up falling out of direct competition—each one is right for certain kinds of users. So which one's right for you?
• Want to run Windows 7 within OS X, and basically nothing else?
• Want to run Windows apps as if they're part of OS X, visually and behaviorally?
• Think a virtual machine should integrate into OS X almost completely, rather than live inside its own window?
• Want to play 3D games in your virtual machine?
Then You Should Use…
Parallels 5! This is a paid solution, and while it's a full virtualization suite—you can run Linux and other OSes from within OS X as well—it's the one most purely dedicated to making running Windows 7 as seamless as possible. Installation is almost completely hands off, and once you've got it up and running, it can actually be themed to look more like OS X. This has the dual effect of making the OS look more natural when it's running in windowed mode (where the OS is isolated to its own window, like an app), and making the so-called "Crystal" mode, which lets you run Windows apps as their own windows in OS X, and which integrates Windows menus into Apple's operating system, such that it's barely even clear that you're not running native apps.
Parallels' strength lies in how thorough it is in trying to make Windows integration seamless. Windows 7's system-wide transparency effects, powered by Aero, work fine out of the box with Parallels; you can enable OS X's multitouch touchpad gestures for MacBooks in the OS with a simple options menu; pulling an installation over from a Boot Camp partition is just a matter of walking through a wizard; sharing files and clipboard items between OSes was trivially easy.
DirectX support is legitimately good enough to actually run a mid-range game without terrible performance degradation. (Games like BioShock or Crysis will run, but unless you've got a top-end iMac, you'll probably suffer from serious slowdowns. If you're serious about gaming on a Mac, just install Windows natively using Boot Camp.) It's kind of like magic!
Parallels' Windows powers are unsurpassed, but come at a cost. First, in dollars: It's $80. Then, in features beyond Windows integration: There aren't a whole lot of appliances—preconfigured packages that let you install other operating systems, like variations of Linux—as compared to VMWare, and there are stability issues; I've had to close down the entire virtual machine a number of times over the course of testing, and I couldn't identify a particular trigger. One second I'd be seamlessly toggling between Internet Explorer and Safari, and the next I'd be trudging through a prolonged virtual machine restart routine.
So yeah, it's worth it, if you've got a handful of Windows apps you can't live without, or if you want to play fairly recent games without booting into a separate partition. [Parallels]
• Want to experiment with more than Windows
• Need bulletproof performance with Windows
• Want to run Windows and Linux apps as if they're part of OS X, albeit without too many interface flourishes?
Then You Should Use…
VMWare Fusion 3! VMWare's virtualization software is a reliable option no matter what you want to do. The way it integrates Windows into OS X is fairly transparent, but not quite as aesthetically consistent as Parallels.
Gaming performance isn't as strong as in Parallels, though 2D rendering—like Windows 7's Aero—runs a bit smoother in Fusion than in any other solution. As with Parallels, Fusion automates the Windows installation process to a degree, and makes importing a Boot Camp installation fairly simple.
VMWare is a workhorse, and for most tasks—be it cross-platform website testing, running Windows versions of Microsoft office, or syncing with a Windows-only device like the Zune HD—it won't let you down.
Tinkerers will find a massive library of preconfigured appliances, so you can try out virtually any operating system you've ever heard of (as long as it's freely available) with little more than a file download and double click. Fusion 3 costs $80. [VMWare]
• Need Windows emulation
• Don't want to pay anything for your virtualization software
• Don't need to do any serious gaming
• Don't mind rougher integration of Windows into OS X
Then You Should Use…
Sun VirtualBox! While the prior two options are paid, and not exactly cheap, VirtualBox is free. Totally. This means that, if you've got a spare Windows license, you can install Windows to run within OS X without spending an extra dime, and without suffering too much of an inconvenience as compared to VMWare or Parallels. (Full Windows 7 installation guide here)