Scheduled to be launched later this year, The Microsoft Windows 7 is touted to be a better OS.
However, unless you are going to buy a new PC that shipped with Windows 7 pre-installed, you may have the worries that your current computer may not be suitable for the new OS.
Hence, Microsot has made available an Upgrade Advisor for you to check your hardware requirements to see if they are up to the par.
To download and install the Upgrade Advisor, go to download.microsoft.com and enter windows 7 upgrade advisor as your search:

Your search should bring you to the download section:
Download the Windows7UpgradeAdvisor.msi and follow the instructions.
However, If you are running Windows XP and do not have .NET Framework 2.0 yet, you will be asked to download and install it. After .NET is installed, you can restart the Upgrade Advisor installation.