It can be very easily done on the iPad itself without going to the computer.
Launch the App Store. Tap on the purchased tab. Find the app that you want to hide. Swipe on the iCloud icon next to the app and a "Hide" button pops up. Tap that and the purchase will be hidden.
EDIT - This only works if you are running iOS 5 on your iPad. Your profile indicates that you are running 4.3.3 so if that is true - you will be out of luck as far as hiding the purchase. I just noticed your profile as soon as I posted. the only thing that you can do to hide the purchase is to sign out of your account on the iPad and the purchased tab will disappear until you sign back in.