The so called plug-in you down loaded was already there. I suspect you only updated it to a level that could display your camera RAW data files.
Each camera model has a unique Camera RAW file definition and Adobe has to continually be updating ACR to accomodate new models.
You RAW image opened in ACR (Adobe Camera RAW).
There are 3 Adjustment areas with their associated icons top right right under:
R
G
B
- "Basic" Which has the array of sliders you first see on the right
- "Detail" Which has basic Sharpening and Noise Reduction sliders.
- and "Camera Calibration" which can be used when you have multiple camea body models
Then across the top of the workspace itself are the available tools (left to right)
- zoom
- move
- white balance tool
- crop
- straighten
- Red Eye removal tool
- Preferences
- and image rotation tools (clockwise/counterclock wise
At the bottom center of the work space is a box labeled "Depth" where you can select the bpp (bits per pixel) also known as 'color depth'.
In your screen shot the bpp was set to 8-bits/channel. There are 3 channels: Red, Green, and Blue (RGB)
8-bits/channel means ACR is showing 256 colors per channel. When changed to 16-bits/Channel ACR will show 65536 colors per channel.
Unfortunately, one of the reasons Elements is so much less expensive than CS4 is it is limited to editing in the 8-bit color depth in the Elements workspace and cannot edit images in a 16-bit color depth, hence the value of learning to do as much editing in ACR as you can possibly accomplish.
CS4's version of ACR has more tools and has 9 adjustment options compared to the 3 mentioned above in Elements
It may be helpful to know that Adobe Lightroom, which is all the rage, has a somewhat expanded version of CS4's ACR photographers can use for layerless and textless image editing.
I highly recommend getting a book that has information on how to use ACR. Scott Kelby's books for Elements contain information on ACR. His Elements 6 book has 40 pages of information on how to use the Elements version of ACR, as an example.