Programs in the Finder/on the desktop

I started having problems in the Finder last night, so I brought my MacBook (running Leopard) to the Genius Bar this afternoon. One of the "Geniuses" fixed part of my problem but also brought in something else which was awkward. He messed around with my User settings and my Finder settings since I had no control over my desktop and all my icons disappeared. Now my desktop is back to normal, but I can't change the icon sizes with the trackpad on my aluminum MacBook. I've also been having a few issues with the "pinching" feature on the trackpad. Also, I noticed when I came home from the Apple Store this afternoon that all of my applications say ".app" behind them. How do I get rid of this? How do I allow icons to be resized on my desktop? How do I reinstall the drivers for the trackpad on my aluminum MacBook? Any help is appreciated!

I can only help you with the extensions part. Go to Finder > Preferences... > Advanced > uncheck "Show all file extensions".

As for the trackpad problem, my best guess would be to check out the Trackpad preference pane in System Preferences.