Hi, and welcome to the forum. It's good to "see" you and I hope you enjoy your visits.
The only way to install Whatsapp onto the iPad2 is to jail break the iPad. Then, you can buy the app from Cydia, the jail breaker's store.
Here's a basic guide on jail breaking and what it is and entails:
http://www.ipadforums.net/showthread.php?t=2838
That ought to get you started to see if jail breaking is for you. Although, I must warn you that, unless you are on iOS 4.3.3 or 5.0.1, there is no way, at this time, to jail break the iPad2. It's a waiting game while we wait to see if/when a jail break will be released for the newest iOS.
Hope some of this helps.
Marilyn