Weird, it didn't restore the mess?
The background should be a simple fix. Just go to the System Preferences, click on the "Desktop" pane, and then just choose the background picture you want (or drag another picture into the well to use that).
As for the Dock, I don't know how it would be "a mess".
To add a screenshot, you need to have it one of the following formats: GIF, JPEG, PNG, or BMP. In addition, it must have one of the following extensions: .gif, .jpg, .png, .bmp, or .jpeg. The screenshot must also be under 100K.
Once the format is correct just click the "Browse..." button under the "Attach file:" area when you reply to a post. Find your file, and select it. Then the dialog should close, and you should see the name of the file in the field next to the "Browse..." button. Then just submit your post.