From your description, I am guessing you are a MobileMe member, and you are syncing your data from your Computer AND your MobileMe account. If you have set up syncing with the latter, you must uncheck all data syncing via iTunes (when your iPad is connected) for your Calendar, and probably your Contacts too.
Are you on a Mac or PC? Not knowing, I can offer some interim advice. On your main computer, open your Calendar application and delete all duplicates. (For PC users, you can do a search for utilities that can do the job for you). Make sure your Calendar is exactly as you would like it to appear on your iPad.
Connect your iPad, and in your iTunes settings, deselect all syncing of the relevant data - your Calendar for sure, and anything else, like Contacts, Notes, etc that would risk duplication, as the Mobile Me account handles this function.Apply.
Once the above is complete and the iPad is no longer connected to your computer, go to your Settings (on the iPad)-Mail, Contacts and Calendar. In this instance, select Calendar settings, and switch them to OFF. Select the option to "Delete from my iPad". This will temporarily erase all your calendar entries. At this point you can check on your main computer that your Calendar is indeed duplicate free, and set up exactly as desired.
Next, back to the same iPad settings - switch the Calendar back to on, and now select the option to "Merge with Mobile Me", as shown here:
In a few moments, your new Calendar/s will appear, fresh and clean, without all those duplicates.
Do the same with your Contacts, Notes, or any other iPad App that has Mobile Me syncing capabilities.
Hope that helps!
Note: the above advice assumes that a Mobile Me account has been set up to handle syncing of the relevant items.
Edit: sorry, from your screenshot I just noticed that you are indeed on a Mac.

Same advice still applies.