Wrong forum or not, I'm answering your question. I don't know how to turn off that huge whole screen thing, other than hitting the back key once you're connected. That said, there's an app, a couple of bucks on the Market (money WELL worth it in my opinion, because this is one of my favorite apps) called Dual Mount SD widget (it shows up as SD share on the widget list). When you touch the widget, it mounts the SD card for you without the huge popup you hate, AND allows you access to all the contents of your SD card on your phone at the same time as your computer. So, for instance, you can listen to music on the SD card while you move files to and from your computer.
The Dual Mount SD widget is on my apps highly recommended list.