Basically, the scripts are run by the browser and make changes for the better, to the page you're viewing. Rather than duplicate others' good work, head over to the User Scripts page at the TechTalk Wiki for full instructions on how to install and activate the scripts.
DD32's All-In-One ABC Forum User Script has the ability to give us back some of the long lost HTML we all miss so much1). Head over there to find out all about it, including configuration instructions once installed.
Dr. ZAx's Image Insertion Script finds where people have linked to images in posts and displays those images directly in the post so you don't have to go clicking links to see them.