One way to find your Windows version is through the System Properties window.

Find your My Computer icon.  It's usually in the top-left corner of your main desktop.  In Windows XP, it's located in the Start Menu.

Right-click the My Computer icon and choose Properties, as pictured below.

The System Properties window appears.

The General tab of the System Properties looks virtually identical on all versions of Windows.

System:

Under the System section you can see the version information.

Method 2:  Start -> Run, winver

Here is a second way to find your Windows version.

On the Desktop, click the Start button and select Run from the menu.

The Run window appears.

Open  =  Enter the letters winver  and click the OK button.

Depending on your version of Windows, one of the screenshots below will appear.