If you’re like a lot of geeks that I know, you have a Mac as your main machine, but often need to drop into Windows to check things like browser compatibility or to use some particular Windows applications. A license for a full install of Windows 7 Ultimate.A MacBook running Mac OS X 10.6.1 (Snow Leopard).Pardon the uncharacteristically nerdy post, but I thought I’d write up a handy way I’d found to run Windows 7 in a seamlessly-integrated virtual machine under Mac OS X 10.6. When I said “for free” here, I meant that virtualization is available at no cost, not that Microsoft’s giving Windows licenses away for free. I thought it’s amazing that a technology I still think of as fairly advanced, virtualizing operating systems on the desktop, has become commoditized enough that free, open source tools are very mature. Update: Since this post got a lot more readers than I expected, it’s become clear to me that the title was unintentionally vague.