Upgrading your OS is fraught with problems and anxiety, and occasionally things will go seriously wrong. But by taking the necessary precautions and assembling the right materials you can upgrade without gaining any grey hairs.
If you've yet to check that your existing hardware is compatible, scan the system requirements and run the Windows 7 Upgrade Advisor Belarc tool. Current Vista users shouldn't have any problems here.
Next, you need to decide between upgrading your current version of Windows or going for a clean, fresh install. The upgrade is easier, since your applications, settings and data travel with you and there's little to do after the install is complete. After a clean or ‘custom' install, you'll have to set up your users and network, reinstall drivers and programs and move your data back into place.
On the other hand, a custom install is cleaner than an upgrade. Windows accumulates junk as you use it. Flushing it out every so often makes sense, as does starting a new version of the OS with a clean slate.
If you're currently using XP, the choice has been made for you. A custom install is the only option. The following instructions apply to both types except where stated.