Common consumer versions of XP and Vista are listed down the side, and the three (out of a total of six) planned versions of Windows 7 likeliest to be used by average consumers on existing PCs are listed across the top. 

Note that ONLY those combinations that intersect in a green box saying “In-Place Upgrade” can be upgraded in a simple way that, in Microsoft’s words, “Keeps your files, settings, and programs intact from your current version of Windows.” 

All of the others, denoted by blue boxes, will require what Microsoft calls a “Custom Install,” also known as a “clean install”–a procedure Microsoft doesn’t even refer to as an “upgrade.” For most average, nontechie consumers whose PCs have a single hard disk, that will require a tedious, painful process with the following steps: Temporarily relocating your personal files to an external drive or other computer, wiping your hard drive clean, then installing Windows 7, then moving your personal files back, then re-installing all of your programs from their original disks or download files, then reinstalling all of their updates and patches that may have been issued since the original installation files were released.

Microsoft will provide a free “Easy Transfer” program to assist in this process, but this software won’t transfer your programs, only your personal files and settings.