This feature was only available on a Jailbroken iPad/iPhone/iPod. But if you want to perform on non Jailbroken iPad so you could use Xcode 4 which coats $5 on MAC App store and you can do it from that.
Now a big secret hidden in the Xcode 4 was revealed by givememind. They really give us a mind.
iPad 2 which not yet Jailbroken and no words are said on the jailbreak yet. Now you can Enable the best feature by just following the steps mentioned below.
Steps to Follow:
Download Xcode 4 form MAC App Store for $5.
Once you are donw with the Xcode 4 Installation now open it and connect your iPad 2 to it. It will show in the Xcode device list.
Now Click on the “Use for development” button. Now it will ask you for your Dev-Account credentials just Cancel it.
Once the developer mode is done, go back into your iPad 2 settings and you will see the new Multi-Tasking Gestures options. Enable it and Enjoy.
Do let us know if it works for you. This will only work on iOS 4.3 and above.