Using iTunes

I'm new to iTunes and Apple products, so this is the problem:

iTunes: I have the latest version for Windows 7. The library is empty, except I just added some videos to it.

Apple iPad 1: I bought this from another person, which is why there were already some files (videos, pictures, etc.) on the iPad. Some of them I found useful, so I want to keep some files.

The Situation: When I connected the iPad to the computer, they recognized it and let me play the files. Somehow the computer don't recognize the iPad as a media storage device (so I can explore the files inside). I want to add the videos I just added to the iTunes's library to the iPad. But I couldn't except using sync, which they'll delete all the videos on the iPad. I can't drag either because for some reasons they don't let me drag the videos to the iPad's video section.

The Question: Is there an easy way to add the videos to the iPad without losing any files and without using sync? I know iTunes help said you can drag to the iPad, but my computer doesn't let me. Because the iPad wasn't a media storage device, I can't copy files to my computer so I can sync later. So can someone show me a way to add videos to an iPad?

Thank you.