What do I add to my code so that there is an image in the comment box? And also what do I put if I want that image to change to a plain color on hover?

.textbox { background: url(URLHERE); }

The answers to these questions are covered in the "Customize your profile! - Codes to help" thread, which is linked to from the sticky in this forum. The board is also currently on the first page, towards the bottom. Locking.