Anil Dash has described how to run Windows 7 on a Mac running OS 10.6 -- as a virtual machine -- for free (after you buy Windows 7, of course). It's not very tricky and, according to Anil, works well. Start by installing Windows 7 in Boot Camp and wait while it grabs the necessary drivers (the duration of this process will vary).
Next, eject the Boot Camp disk and enter a few simple Terminal commands. You'll also need VirtualBox, which is free and open source virtualization software. Once you're done in Terminal, launch VirtualBox and browse to the file you made with Terminal. Read Anil's article for the details.
As today is Windows 7 launch day, we're interested in hearing from anyone who has installed it on their Mac, either via Boot Camp or virtualization.
For more, read Christina's post on installing Windows 7 on a Mac (at Download Squad), or Steve's take here. You can get your absolute fill of Win7 coverage all day today at DLS.