Whether you want to set up a dual-boot system, you're ready to migrate all the way to Windows 7 RC from XP, or something in between, here's what you need to know.
Dual Boot Windows 7 with XP or Vista
We showed you how to do this back when the Windows 7 Beta was released, but if you were waiting for a slightly more stable Win7 release, you might be ready to dual boot Windows 7 with XP or Vista. This is generally the method of testing Windows 7 that we'd recommend, since it allows you to try out everything Windows 7 RC has to offer without entirely giving up your trusty old operating system.
Upgrade from Windows 7 Beta to RC
If you've already taken the plunge with the Windows 7 Beta, chances are you don't really want to set everything up all over again when you install Windows 7 RC. Unfortunately for you, Microsoft recommends a fresh install over an upgrade, and in fact, if you want to upgrade rather than install from scratch, you'll need to perform a simple hack. Likewise, you'll have to perform an in-kind upgrade, meaning you can't go from 32-bit Vista to a 64-bit Windows 7 install without doing a clean install.
Upgrade from Vista to Windows 7
There's really nothing to this; Windows 7 provides a direct upgrade path to Windows 7 from Vista, which means that when you install Windows 7, all you need to do is select the Upgrade option when you run the Windows 7 installation. Note: Windows 7 requires that you've installed Vista Service Pack 1 in order to upgrade.
Migrate from Windows XP to Windows 7
Unfortunately Windows 7 doesn't have a direct upgrade path from XP, meaning if you're going to take the full plunge from XP to Windows 7, you've got to do some work on your own if you're hoping to migrate your files and settings from XP to Win7. Luckily Microsoft has a video detailing how to migrate from Windows XP to Windows 7 using the User State Migration Tool, an app from Microsoft that moves all your desktop settings, application settings, and files to a new Windows installation. (Also found via Life Rocks 2.0)
If you've made the early adopter move to Windows 7 and you took a different upgrade route, let's hear more about how you did it in the comments.