Whatsapp is not supported on the iPad (per the developer). The only way you can install Whatsapp on your iPad is to (1) jail break it and (2) install some tweaks/do some fiddling with it. See this link for more details: http://www.ipadforums.net/showthread.php?t=89303
And, since this has been asked (and answered) before, we'll close this thread now. Thanks for your understanding.