Lets work backwards from your questions.
You cannot prevent the iPad from transferring content into iTunes. It is supposed to do that so that all of the purchased content on your iPad is stored in your iTunes library. That's for your protection. If you experience problems with the iPad and need to restore, all of your purchased content will be on your computer so that you can sync it back again. You could download much of your paid content again, but that take hours and hours to do.
Try this. First turn off auto syncing in iTunes. If you are running Windows launch iTunes and go to Edit>Preferences>Devices>Prevent iPods, iPhones and iPads from automatically syncing. Click OK. Quit iTunes.
Now connect your iPad to your computer and you will have to launch iTunes on your own. From what you have stated already, you know how to select (click on) your iPad name under the devices heading. After you click on the iPad name, click on the Movies or TV Shows tab at the top of the iTunes window on the right. Uncheck Sync Movies or uncheck Sync TV shows. Then click on Apply in the lower right corner of the iTunes window. That will sync the iPad and remove all of the TV shows and Movies from The iPad.
if you want to select certain shows or movies to sync, keep the Sync Movies or TV shows heading checked and then uncheck the ones that you want to remove. Click on Apply, and the ones that are checked will sync - the ones that are unchecked will be removed.
You can do this in every tab in iTunes and select the exact content that you want to sync. Once you set your syncing preferences, iTunes will remember what you have selected to sync and what you have deselected to sync.
If you want to auto sync again, go back to Edit>Preferences>Devices and uncheck Prevent iPods, iPhones and iPads from syncing automatically.
I have never synced automatically, I prefer to choose my content and initiate the sync on my own.
