(Reproduced from: http://www.microsoft.com/windows/windows-7/upgrade-advisor.aspx)
In general, if your PC can run Windows Vista, it can run Windows 7. But if you’re not running Windows Vista, or are just not sure if your system is ready to run Windows 7, there’s a quick way to do a simple check.

Just download, install, and run the Windows 7 Upgrade Advisor Beta. You’ll get a report telling you if your PC can run Windows 7 and if there are any known compatibility issues. If an issue can be resolved, you’ll get suggestions for next steps. For example, it may let you know that you need an updated driver for your printer and where to get it.

Note: Information about your PC will be sent back to Microsoft; however, no information will be used to identify or contact you. For more information, read our privacy statement.
Before you begin

Before you run the Windows 7 Upgrade Advisor Beta, be sure to plug in any USB devices or other devices such as printers, external hard drives, or scanners that are regularly used with the PC you’re evaluating.

Download the Windows 7 Upgrade Advisor Beta

Important: The Windows 7 Upgrade Advisor Beta is a pre-release version and is available in U.S. English only. While we consider this a stable and high-quality beta, it’s not the finished product.