If your keyboard has a Windows key you can press the Windows key and the R key together to execute a command. Just write cmd and hit enter, this opens the Windows console. Then navigate to your namecoin folder and to execute a command write:
and hit enter. The help command gives you a list of all the commands (namecoind.exe help).
If your keyboard doesn't have a Windows key but you are using Vista or Windows 7 you can just click on Window's Start button in the task bar and enter cmd into the search field, then hit enter. On Windows XP you can use the Alt + F2 key if I remember correctly.