If you do like the user two posts above me said, everything will be fine, and you'll get the drag and drop interface that you're looking for. You'll be easily able to take playlists, movies and straight up songs and drag and drop them onto the ipod. You'll also be able to drag things off if you don't want them any more. Simply click on the iphone in itunes, and under Summary tab you'll see a check box that says "manually update music".
As for auto-sync (which it seems that you don't like much in any case) make sure that you go under the video tab, check Sync Movies, and underneath, check all movies. Do the same for music. This way you will not have to check the boxes beside each and every movie in the preferences. Do the same under Music. I understand that you did this before, but make sure that you click on apply in the bottom right hand part of the window.
Also, If you'd like to turn auto-sync off when you plug your iphone in again, hold down command and option, and continue to hold it until the iphone pops up in itunes. This will only turn it off for this instance, so you'll still have to go into the preferences and change the settings.
I hope that this clears things up for you.