Windows 7 only allows you to upgrade directly from Vista, so if you are looking to switch from XP you are out of luck. Thankfully the built-in Easy Transfer tool makes the upgrade process much easier.
Over at the How-To Geek site (my home away from Lifehacker), blogger Mysticgeek has put together a full guide to using Windows Easy Transfer to move all of your files and settings from your XP computer to your new Windows 7 PC—though the tool can be used from Vista, or even if you decided to dual-boot Windows 7 with XP or Vista.
The principles are simple: just run the Easy Transfer wizard (included on the Windows 7 disc) on the computer you want to migrate settings from, choose everything you want to transfer, and save the Easy Transfer backup file to a drive. Once you've installed Windows 7, you can run the Easy Transfer wizard to restore all of the settings from the backup file to your new computer. The tool only packages documents, settings, and things like wallpaper—so you'll have to reinstall your applications—but it works surprisingly well for helping migrate your settings.
Hit the link for the full walk-through, or check out our guide to upgrading to the Windows 7 RC, or how to upgrade the Windows 7 RC to the final RTM release.