Windows X's Live recommends:
Before and after making any changes to your system: Check Windows for registry errors.
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For those who have not installed the Release Candidate of Windows 7 and prefer to take their time (the vast majority eventually), Microsoft has launched a beta version of its Windows 7 Upgrade Advisor. This application analyzes the configuration of the user to report if the machine is ready for Windows 7. The analysis is both hardware and software, and it starts by checking if the minimum is present:

• A 32 or 64 bits to at least 1 GHz
• 1 GB of RAM in 32-bit, 2 GB 64-bit
• 16 GB on the hard disk into 32 bits, 20 bits 64 GB
• A DirectX 9 GPU with WDDM driver 1.0 (or higher)

Microsoft recommends that users absolutely every limb peripheral equipment before starting the software. Regarding the analysis software, it provides a report on the programs installed to indicate if they are compatible with the state in Windows 7. The information will be used for resettlement on a new, or in case of an update

The beta of Windows 7 Upgrade Advisor (in English only) can be downloaded from this page.