you've come across the annoying T8 screws with a pin in them.
That makes them a T8H screw.
Here is the tutorial about dealing with them.
Step 1: Pin Pin Pin!
Check out those pesky T8H screws!
The easiest thing would be getting a T8H screwdriver, but they are hard to come by.
Here's the next best thing and it's pretty simple.
Things you'll need:
Small Flat Head Eyeglass screwdriver,
also known as watch screwdrivers or watchmaker screwdrivers(dollar store)
T8 Screwdriver (auto store, computer parts store, or radioshack) -
(I personally think the T9 fits better, but w/e is easier to find will work)
xbox 360 controller that you want to open