It looks like your PATH isn't setup correctly. Sometimes this happens when you install Python in a specific folder instead of the default C:Python folder (e.g. C:Python27)
To setup your PATH, right click on 'My Computer' and click 'Properties', then in the 'System Properties' click on the 'Advanced' tab. In the 'System variables' section, you'll see a variable called 'Path'. Now add where you installed Python to that list (additional items are appended with a semicolon).
For example, if you installed on C:Program FilesPython27 then you would add ";C:Program FilesPython27" to your PATH variable.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…