Microsoft offers a free and that is the best place to begin your upgrade odyssey. Also, here is a link to the . You may want to read it before making your upgrade decision.
Be warned: users get to upgrade while XP users will migrate to the new OS. The difference is important, as you will see.
Windows Vista Users -- If you have survived this long with Windows Vista, you may be in no hurry to upgrade. People who like Vista may actually consider a step backwards in some regards.
The good news is that you can upgrade a Windows Vista machine to Windows 7 with a minimum of difficulty. Also, a machine that runs Vista may run Windows 7 a bit faster.
Users -- On the Windows Upgrade Advisor page, Microsoft states: "If your PC can run Windows Vista, it can probably run Windows 7, but it's still a good idea to use the Windows 7 Upgrade Advisor."